None of the teams in the B1G-W have been mathematically eliminated but that will likely start this weekend.
If Wisconsin beat Illinois the Badgers will move to 5-0 and the Illini to 0-5 thus mathematically eliminating the Illini.
The Iowa/Minnesota loser will fall to 1-4 so a Wisconsin win this weekend would leave them mathematically with a chance to tie but not win outright.
Wisconsin's "magic number*" is three.
*Magic number: The combined number of Wisconsin wins and losses by their closest competitor necessary for the Badgers to clinch a spot in Indianapolis. Ie, if Wisconsin wins three more games they will finish no worse than 7-2 and that would be no worse than a tie with the Nebraska/Northwestern winner. Wisconsin already defeated both the Cornhuskers and the Wildcats so 7-2 would guarantee them a spot in Indianapolis.
The earliest that Wisconsin could possibly clinch is next week. If they win their next two games (@ILL, @IU) they will move to 6-0. That would do it so long as Nebraska (@PU, vNU), Northwestern (vMSU, @UNL), Iowa (vMN, @tOSU) and Minnesota (@Iowa, @M) each lose at least one of their next two games.