Hi and welcome.
Really sorry to hear you experienced such a horrid and scary situation. Seizure are very rare, or they should be so his diabetes management really needs looking at, so it is great that you are trying to get an appointment if he has had so many and in my view, 6 seizures in 10 years is way too many. It might be worth asking about a DAFNE course which is an intensive education course for keeping yourself safe with insulin in all manner of everyday situations and learning all the factors which can cause your levels to drop.
First to consider is why it happened, so that you can take steps to try to prevent it in similar situations in the future. Not meaning to be personal, but had he done any physical activity before the nap. Physical activity can make any insulin in your system much more effective and needs to be considered if you exercise or do something physical whilst your mealtime insulin is still active, so up to 4-5 hours after injecting for a meal. Many people don't consider that things like sex are physical activity and often it can be spontaneous, so you don't consider it when you inject your meal time insulin like you would if you were intending to go for a run or a swim or a game of football in the afternoon. Most of us reduce our meal time insulin if we plan to exercise afterwards or make sure to top up with carbs if it is unplanned activity.
Alcohol can also lower levels and cause hypos as can hot weather.
It concerns me that he had to get up to get his hypo treatment. It really is important to have them within reach at all times but particularly when waking from sleep as a hypo in that situation can make you much more vulnerable. I keep my hypo treatment of choice (jelly babies) on me at all times and on the bedside table during the night so I can literally reach across and get them without even sitting up or putting the light on. I also have them in the bathroom as a hot bath or shower, particularly after exercise, can drop your levels quickly. I personally wouldn't find a can of coke particularly practical because there is quite a volume to drink to get enough glucose, plus I can't drink fizzy stuff fast and I would have to sit up to drink it whereas I can chew jelly babies whilst lying down. As
@SB2015 says, your hypo treatment will absorb quicker in your mouth than gulping it straight down so perhaps the gel sachet's would have been more effective if he had held them in his mouth. The mouth is also closer to the brain than the stomach so the glucose absorbed by the cells in the mouth will get to the brain quicker than from the stomach. 3 well chewed jelly babies or 4-5 glucose tablets should be very effective in bringing levels up..... BUT you will not see that recovery on Libre for quite some time and should absolutely not rely on Libre or other CGM (Constant Glucose Monitor) for assessing recovery from a hypo. You should always revert to finger pricking 15 mins after treating a hypo to check recovery because the way the sensors work means that it will almost always show your levels continuing to drop 15 mins after hypo treatment and cause you to panic and over treat them which will result in a high later which is not good for the body either. So finger prick kit should be close to hand too in these situations to check your blood for recovery and not rely on the sensor at these times. Having a good disciplined routine with hypo treatment is important but prevention is obviously better.
You mention the Libre keeps dropping out..... Does he have other Bluetooth devices paired with his phone? If so, that might be the issue as I believe Libre is not a strong signal. Keeping the phone close is obviously also important particularly in situations like this when your life might literally depend on it. Personally I use the dedicated Libre reader rather than the phone app and never have a problem with not getting alarms. I have to scan to get readings rather than get them automatically like they do with the phone app but the alarms are really reliable and it isn't affected by other BT devices that might be connected to the phone or OS updates which can throw the LibreLink app into a wobble from time to time. You can also use the Libre reader as a BG meter. Putting some effort into sorting the problem with his phone dropping connection should definitely be a priority. And also having his low alarm set higher. The fact that he is realising too late that he is low suggests that his hypo awareness is affected and he perhaps needs to put some work into improving that by running his levels a bit higher for a while, so his body learns to spot low BG before it gets too low and warn him earlier, even if the Libre has dropped out. Running low too often can cause the brain to get used to these lower levels as being normal and erode the normal early hypo awareness signs. Good hypo awareness would be getting those signs in the low 4s which gives you time to respond well before things get critical. If your partner's body isn't giving him warning signs until he is close to passing out/fitting, then he needs to work on improving his hypo awareness by running consistently higher.... not talking silly high but maybe keeping above 6 or even 7 as much as possible.
Finally, a pump might be the answer and having seizures should probably qualify him, so that is something to consider asking about when he sees his nurse.
Anyway, those are just a few of the things that occurred to me whilst reading your post. I hope some of them are helpful as this situation is not normal for people with Type 1 and with help and some effort on his part he should be able to improve things and hopefully significantly reduce the risk of it occurring again. I can totally understand how scary and unsettling it must be for you and it is great that you want to support him with resolving it, but ultimately he has to make some effort and to know that it isn't normal for this to happen and just accept it as part of living with Type 1, especially with modern insulins and technology but you do need to put aside some time and "headspace" to sort it out.