I would highly advise in a policy against account detail sharing. In this benign case, it wouldn't seem to be much of an issue (given you have no problems with the person later down the road). Yet, we have to look at the big picture (especially when it comes to game policies and rules), and consider all instances account information would be shared. We then get in to the problem of politics and handling each case as individual situations. That would mean the GMs would have to make judgement calls per case (not to mention the investigating they would have to do for each). That could be a monster of an issue when the player base grows. If there is a firm policy set in place now, it would eliminate the above issues all together. Given the "Holiday" policy that the GMs are looking at implementing, there would be next to no reason to share account information other than simply gaining a slight edge (your city progression) in the time you woule be absent. This would allow the GMs to have considerably more time focusing on game improvements, game issues (bugs/glitches), and management.
there's my two cents :P