Defensively Huddlestone and Parker would be fine, although not as good as Dembele and Parker and arguably not as good as Huddlestone and Dembele. Obviously not as good as Sandro and anyone.
The problem would be going forward. Huddlestone rarely ventures into the final third. Parker does so at times, but seems to develop some kind of anxiety when he gets close to the box so he's not much use in those positions. Didn't we play them together at one point earlier this season and see exactly that?
I agree with punk_is_back in principle. Overall Dembele is at least as good as Parker at winning the ball on current form. Perhaps Parker is better purely at tackling, but Dembele's quickness makes him much better at closing down and he's stronger in shoulder to shoulder situations too. Overall as good a ball winner imo. Stats also support this notion with Dembele racking up more tackles per game than Parker this season
http://www.whoscored.com/Teams/30
Perhaps Parker was better, in the first half of last season.