It's definitely happening unless there's a pitch invasion, in which case it'll be up to the stadium manager and OB. This is what SB said on the BBS thread:

We have agreed with Tony that the players will come off the pitch and come back on for a lap if neither set of fans have come onto the pitch. The Police and Stadium manager will have the final say on the night should any fans try to get on the pitch.

I hope that as many fans as possible will be able to remain behind and give the lads the ovation they deserve after their great efforts this season.

[Link]

"You can feel the stadium jumping. The stadium is actually physically moving up and down"
FA Cup MOTD 24/4/16