Most other MMO's i've played have a repossession system for situations like this, all that happens is the plot goes back up for sale and all your stuff that was inside can be reclaimed at an npc, along with a voucher to get another plot. Of course those MMO's had a rent system for housing, so it wasn't really repossession due to inactivity, but due to running out of rent on the plot.

I would fully support this though, if I was gone for months on end, I'd prefer my plot actually be used by someone that plays the game, as long as I was able to obtain all my stuff and not have to pay full price for another plot when/if I came back.