Where did you see this? $500M/yr was the lowest estimate I have seen.
Kevetrin is very hard to value. Given the enormous deals on pre-clinical cancer drugs we've been seeing over the past decade, I think Kevetrin is worth well over $100 million. I don't know what Leo values it at and I don't know what BP values it at though. It's too hard for me to consider it any thing other than an upside, wild card sweetener for a full company buyout.
I'd love to see a billion dollar deal done on B-OM/IBD. It's certainly very possible but it takes a bit more faith to get there. The numbers I suggested run significantly higher than the doom/gloom being posted here and are still easily digestible by all but the most negative skeptics. I don't think we could get $1 billion in a full takeout at this time.