Prem's investment was about the same as most everyone else's at that time. Smartphones were HUGE and BlackBerry was still a pretty big player.... all they had to do was get the new OS release and they'd be back at $50 a share. He wasn't planning some long term play.
I don't think Prem really understood the business or the level of incompetence within the company. He gambled on what should have been a pretty good bet, and he lost.....
Maybe BlackBerry is sold and he breaks even, maybe in five years they are a small software company that's worth $16 a share and he get his money back... either way he has tied up a lot of his resources with no real gain (if not a small loss).