Any bike can be a "last bike" if you quit bicycling, for whatever reason, before you get the urge to buy a new one.

All components wear out and need to be replaced, eventually. So your question becomes what frame will last the longest? Like other respondents, a steel touring bike would be one of my top choices. But if you want to go on rougher roads, you might want to look at gravel bikes (if you can find one geared appropriately low), or even a rigid mountain bike.