Friday, we looked at where Michael Crabtree ranks on a list of the top 10 potential free-agent wide receivers in 2015.It's a strong class. In ESPN Insider Mike Sando's ranking , based on the opinions of NFL general managers and coaches, the San Francisco 49ers standout is No. 3 on the list.If Crabtree isn't re-signed or given the franchise tag, he would be very popular on the open market. So, it begs the question: What would the 49ers do if Crabtree leaves?