Hello and welcome!
The problem is that in a grid down type of situation repeaters can be down as well because most are powered from the grid, although some have back up batteries or generators maybe solar even. So they can not be relied on for emergency communications planning. VHF and UHF (GMRS is UHF) are basically line of sight communications. If the two antennas can see each other then they can talk. If you can both get enough altitude as in hill top to hill top you may get 100 miles or more. 250 miles? Not likely. For that distance you will need to look to the ham radio world.
There is a lot to learn about radio comms for it to be effective in emergencies or just to be competent with it in general.
Look for better quality radios for emergency use. They need to be reliable.