We had a discussion in another thread not very long ago about changing the way mothballing works. Basically, you could mothball a ship anywhere but it would not stay 'pristine' if it wasn't in a sector with a spaceyard. And it could only be UNmothballed by a spaceyard. So, if you had an emergency of some sort you could effectively abandon a ship by mothballing it. But it would get 'damaged' each turn until it was completely damaged -- or recovered by a spaceyard ship -- and would be destroyed just as if blown up in combat.
Of course, a ship just drifting in space should be open for anyone to board and take. So you would effectively have derelicts, too. And 'salvage' in space!