I wouldn't say they "should" have them, but if it's set in a realistic environment that covers a wide area, there would be vehicles there in real life so they should be in the game as well. Mountains, caves, etc, probably not so much. But a city or an island or a big expanse of desert and yes, a vehicle would be completely necessary.
I'll be interested in this if they can fix the issues that FC2 had. I loved the way it looked and the amount of environmental carnage you could cause, routing enemies out of hiding spots with fire. But the constant respawning bugged me as well - especially when you know that the reason everyone saw you as an enemy was because of lazy programming. If you clear out an area for one side, you should be able to pass through there freely as an ally. I'd rather have a single much longer and harder battle to clear it, than have to suffer a few minutes of stupidity every time I want to get to the next mission point.
Oh, and fix bugs. So many bugs.