This may be a question for your vet. I think it's hard for any of us to answer since we don't know your kitty's history or how he got to such a high dose.
I'm assuming you won't be able to shoot for two full days and we're not talking about missing a dose on four separate occasions. If your kitty needs this high a dose of insulin to keep sugars in the normal range, skipping for two days could cause high blood sugar which may result in a few different things.
On the low end of what I might worry about would be sugar spilling into the urine causing a urinary tract infection and in turn causing high BGs for a while. On the high end of my worries I'd be concerned about ketones forming and coming home to a kitty in diabetic ketoacidosis. This is just two things I can think of quickly.
I guess I would add that no insulin would mean the sugar would build up in the system and then his body would work frantically to remove it so he'd be using the litter box like crazy and be very thirsty, if you were out of town for two days, he could run out of water during this rush of sugar and dehydration would be another concern.
I'm not a vet or an expert, these are simply my thoughts on why I would not skip four doses in a row.
I hope that you stick around FDMB and if you're not already home testing, check out some of the information here on that and on diet and ask lots of questions. Even if you've been at this for a long time, you may find some of the information here really helpful.