Sometimes a wiki just closes as part of WikiLifeCycle. 

Possible Reasons:
* Just a limited time project or experiment
* TargetUnreachable
* Host burnout (conflicts, trolls, lack of positive feedback)
* Developer burnout (keep up with developments, e. g. spam blocking)
* money problems
* key participants move to new platform
* ...

Alternatives:
* Keep the wiki, either static or FishBowl""ed (GatedCommunity).
* ...

Aspects:
* It is fair to give contributors enough time to save or redraw their contributions.
* It may be seen as a warning to the online community that the patience and energy of a host may be limited
* ...

Examples:
* AndStuffWiki in Aug04. 
* KnowHowWiki Dec2004
* WhyClublet (date?) - FishBowl""ed; later reopened on an invitational basis
*...