There is a need for a 3/5ths quorum ONLY for tax/appropriations bills. For bills that do not involve Wisc spending money, only a simple majority is needed for a quorum.
All the Repubs need to do is word their bills as non-appropriations bills, pass them, and send them to the Gov for signature. Bills like removing a need for the state to forward union dues is not an appropriation.
People should put pressure on the Repub senators to declare a quorum for non-fiscal bills and just start passing an agenda rapid-fire. Starting with making Wisc a right-to-work state, and passing Vermont-style no-license CCW.
Indeed, is there any reason the Republicans shouldn't use the Democrats' departure to their advantage? Frankly, it would seem this should provide an opportunity to pass a lot more no-compromise legislation than would otherwise be possible.