Yep, if we lose to Sheffield, then it's not all over, but it won't be looking great for Fax making the top 4. We'd have to win our last three games and hope Sheffield lost their last 3 (not impossible, given the opposition), or alternatively, hope that Fev lose a couple of their last four games. It would probably come down to points difference then (Fax have the advantage there, by 39 points at the moment).
Fax beat Sheffield, and it's all on between the three teams, with London needing two of us slip up pretty badly (as well as winning their remaining games).
If Fax win all 4 games, it's mathematically possible we could still end up 5th, but both Fev and Sheffield would have to win all their games (other than when they play each other). The loser of Fev/Sheffield would then be on 32 points with us (the winner on 34) and the 4th spot down to points difference.
Ain't it so much better this year with something to play for!!!