There aren't a lot of people here who have substantial experience editing Wikipedia, though. That's probably why it's difficult to get responses here on the topic.
In response to your original post, it's not usually necessary to change the content of an admin's user page once they become inactive. A bureaucrat will perform the necessary procedural removal of admin privileges behind the scenes. While it is possible for someone to subsequently edit their user pages, it's not typically done without getting that user's permission first.
Personally I would strongly discourage editing anyone else's user page without their permission, unless you can prove why it would be necessary (for example, if an inactive admin still has a template or category on their user page that places them in an active admin category). Alternatively, you can always discuss it with the editor who reverted your previous edits, or get further advice at the WP teahouse (they're really helpful for any editing-related questions on Wikipedia). Hope this helps.
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It is easy to go down into Hell;
Night and day, the gates of dark Death stand wide;
But to climb back again, to retrace one's steps to the upper air –
There's the rub, the task.
– Virgil, The Aeneid (Book VI)