The rest of the Wisconsin constitution uses the term "elected officer" when it also means members of the legislature. This refers to "office", not "elected officer" so you'll need something more than your interpretation to tell us if this applies to the legislature ~ which it may well not.
Got a court decision or a prior legislative action?
Or, maybe you can look and see if the Constitution already carries some other relevant section about filling vacant seats.
What Good Can a Handgun Do Against An Army?
http://www.freerepublic.com/focus/f-backroom/2312894/posts
You may be right about the legal definition, but I’m sure they won’t do it anyhow. BUT, the mere threat of invoking this action may serve to bring the fleebaggers in. According to media people who are talking with them, they had no endgame in mind when they took off, it was just “Road trip!”, thinking somehow their stunt would turn the political tide in their direction. Now I suspect their resolve is beginning to weaken and maybe they’ll start looking for an excuse to come back (e.g. “We had to keep the mean Republicans from declaring our seats vacant and replacing us”.