It's actually not terribly difficult to see Purdue in the B1G Championship game even without beating Sparty. The key is that Wisconsin and Iowa BOTH have to go to Happy Valley. Then if you take home teams winning all of the "tough" games with 1 easy exception, you have Purdue winning the West outright, without any tiebreakers.
Purdue (3-1): @MSU L, IOWA W, @Minn W, WISC W, @Ind W 7-2
Wisconsin (3-1): @NW W, RUT W, @PSU L, @Pur L, MINN W 6-3
Iowa (3-1): @PSU L, @Pur L, NW W, @Ill W, NEB W 6-3
Northwestern (4-1): WIS L, @Iowa L, @Minn W, ILL W 6-3
The easy home/road exception is Wisconsin winning in Evanston. Not a stretch at all. The biggest stretch might be Minnesota not winning one of their games against 3 of these 4, namely against Purdue. If you reverse that, and get a 4-team tiebreaker, I don't know where the tiebreaker goes. Eventually it has to go to overall record where Purdue would lose to Iowa (and Wisconsin).
Purdue (3-1): @MSU L, IOWA W, @Minn W, WISC W, @Ind W 7-2
Wisconsin (3-1): @NW W, RUT W, @PSU L, @Pur L, MINN W 6-3
Iowa (3-1): @PSU L, @Pur L, NW W, @Ill W, NEB W 6-3
Northwestern (4-1): WIS L, @Iowa L, @Minn W, ILL W 6-3
The easy home/road exception is Wisconsin winning in Evanston. Not a stretch at all. The biggest stretch might be Minnesota not winning one of their games against 3 of these 4, namely against Purdue. If you reverse that, and get a 4-team tiebreaker, I don't know where the tiebreaker goes. Eventually it has to go to overall record where Purdue would lose to Iowa (and Wisconsin).