Without home testing, you really do not know when he is going too low to do anything about it - well, until it gets so bad he ends up in the emergency room. They don't usually show visible signs of hypo until it is really bad. Insulin needs can change rapidly, so periodic vet visits being the only time glucose is checked is a bit dangerous. Fructosamine tests give you an average over a couple of weeks, so they don't really show you how well a dose is working. Glucose levels can be on a roller coaster... way up and way down..and the average won't show you that. Curves done in a vet's office are impacted by stress, so they do not tend to be extremely accurate and may result in a dose being set too high. Anyway, I know this is not the kind of advice you asked for, but I had to mention it, especially since you mentioned being concerned with him going too low.
It sounds like you have already decided that you cannot have someone come over, and you cannot board him, and you cannot take him with you. So, I guess you know that the only options left are you staying home or him not getting his insulin. Without knowing how long he has been on insulin, what his dose is, whether he has had any issues with ketones and how his glucose numbers are looking lately, it really is not possible to give you any kind of informed advice/opinion on letting him go without insulin for a full week. I can only say that when Mia was on ProZinc, I would not have let her go a week without her insulin. Even now when she is on Levemir and her numbers are consistently really good, I might let her go two or three days without insulin if I had to, but I would not want to go a week.
If you are going to be gone a full week, surely you have someone coming by to handle food and litter and just check in. Is that someone your cat knows? If not, could they start visiting before you are gone to let him get used to them? Would they be willing to stay at your home while you are gone or maybe do multiple visits in a day to check in?
