Blogs are normally run by a single person (unless for a publication), wikis are normally run by a community. Hence someone can discover a wiki and edit it long after its original creators have departed, so long as it wasn’t set to private. The best that discoverers of an old blog can do is to write in the comments section. Maybe reblog it and hope that pingbacks (remember those?) get triggered.

The implicit invitation to collaborate is what gives the wiki longevity and the possibility of resurrection.