Ray was the 24th most efficient player in terms of points per possession in the NBA last year (playing injured) after being 10th best the year before. He was rated 42nd best defensively by Synergy in points per possession. There's nothing in those numbers that suggests that he's all washed up if he recovers from his injury which I expect he will
When we face him, we'll have the following options. Cover him with Rondo, who is a very good help defender, but not great running through screens. Cover him with Bradley, who would be better used on Wade and may not be on the floor at the end of games any way. Bradley will shut Allen down, but Rondo won't shut Wade down. Cover him with Terry, whose offense we'll need at the end of games, but who is not a good defensive player, or cover him with Lee, who isn't as good a defender as Rondo or Bradley and probably isn't on the floor at the end of games as his offense isn't that good - a spot up shooter who can be defended easily.
I don't see any of those match-ups as being as good for us as having Ray on the floor at the end of games. I have to think that Terry's finishing games at this point because he's a much better offensive player than Lee or Bradley, but Allen's a better player at both ends of the floor than Terry.
I do think we can beat the Heat because our bench is so much better than last year, I assume PP will be healthy for the p[layoffs this year, and Terry was the best alternative to Allen we could have gotten by far. However, Allen's likely going to on the floor over Chalmers during crunch time, and that's a big improvement for them, assuming he's healthy, and it's not an easy match-up for us.