This is somewhat similar to "How do you deal with missing players?", but I'm looking to address slightly different issues. Also, this query is about longer breaks than the one or two sessions described in the other question.
Without going into much detail of the whys and hows, our chat-based game has encountered a situation in which some of our Player Characters will be left out of the story going forward for an indefinite period of time. Still, it is understood that there may be a later time in which these characters could return to the story. This could be one or two encounters down the road, or it could be much later.
In the case of "much later", the rest of the party will likely have gained several levels and much loot by the time of the prodigal character's return. What is a good, balanced way to bring the returning character back up to speed with the rest of the group?
EDIT: A lot of the answers seem to be missing the spirit of this question. I'm not asking whether to bring a returning character up to level/equipment speed with the rest of the group - the answer here is yes, we're going to do it - but rather how to do it in such a way that preserves the balance of a natural game progression.
I've also decided to re-tag this as D&D4e-specific. It seems leaving the question generic (though I believe it could serve a good reference for other systems) is not producing very useful answers.