I dunno about getting stuck with 2WD; almost never happened to me when my van was 2WD. But a locker isn't a bad idea; it could really help in some situations. But departure clearance was often more of an issue offroad for me. Pretty common to have steep exits out of the washes I'd find myself in, and if your rear wheels aren't planted it doesn't matter if you have a locker back there.
The other huge benefit was low range. Again, you can get some of this by changing gear ratios and upsizing wheels as much as possible, but then you sacrifice on the highway.
But don't fret. In my experience the piece of equipment behind the wheel is probably more important than the stuff under the van....
A good driver can get a 2WD lots of places that lesser drivers need 4WD for.