I say no trophy until the Illinois game is over---not that anyone cares what I think.
Slightly off-topic, but does anyone remember the end of the 1998 season? Purdue was playing MSU in East Lansing. Sparty had already wrapped up a share of the B1G championship but had to beat Purdue or share the title with Illinois. MSU unfurled a banner before the game, and right on cue, Purdue went on to beat Sparty 99-96 in OT--one of the most epic college basketball games I've ever seen. The announcers had some fun with that.
It probably won't be that dramatic this year, but I still say no trophy, no banners, no t-shirts, no hats, no net cutting, no confetti, no public celebration of any kind until Purdue beats Illinois.
Just my $.02.