You are correct that the senate is unlikely to reconvee until January, by which time the GOP will have retaken the majority (with a pickup of at least 2 seats among the half of the senate seats up for election in November).
But it is not correct to say that the Democrat Lehman (assuming that his lead holds) will never be seated. He was elected to serve out the remainder of the term, which expires after the November 2014 elections. Whoever runs for the Republicans in that senate district in November 2014 (maybe a Wanggaard comeback) is sure to win, given that the district was redrawn to exclude the City of Racine and to replace it with heavily Republican rural and suburban precincts from Racine and Kenosha Counties, but Lehman will hold the seat until January 2015 .
They could run a recall election against him in 1 year, and with the new district drawing, they could easily beat him.
Of course, that assumes a judge doesn’t force them to run the recall using the old maps.
Map changes for staggered elections are strange, because it means some people don’t get to vote at all, and others get to vote for their new representative while another representative they voted for remains in office.