I used 100% AI for maybe 30+ years - with a 60 day window. Yes, we would have a cow or two open. Some would be bred and slip the calf later. But, you will have the exact same problem with using a bull. Unless you keep the bull with them year round, you will have open cows.
We went to AI'ing 42 days, then a clean up bull for 24 days. Makes life easier, but we still ended up with an open one or more. I am back to 100% AI for past two years.
We calve spring & fall, so if I have a good cow come up open, I can give her a 2nd chance and only lose 6 months on her. Open again, shipped. I don't have any "border-line" cows sitting around waiting for an excuse to get rid of. I have to think long & hard about shipping one of my cows, because they are hard to replace. If I have a bad one, she gets shipped right away. I do have some cows that have minor problems (like a problem with a foot or don't like their udder), so I put an embryo in them, because I don't want their genetics to continue.
AI is a commitment of TIME. You have to decide if the value of your calves out-weigh the effort.