I've been thinking about this. I think the best
solution is to allow the
deletion of a user, with all of the user's edits assigned to a single
special user (say, "Trash" or "Junk" or whatever). That way, the
references all over wiki would be intact, i.e. they would still point to
somewhere (in this case, the special user) and there would be no need to
rename dozens or hundreds of accounts to things like "renamed-spammer-1"
- the deletion script/specialpage would do the reassignment automagically.
Technically, that ought to work. Legally, however, you're asking for
trouble. Unless contributions are made under the condition that all
rights are released either to public domain or the owner of the site,
then attribution is almost certainly required.