Ian Bell's got a pretty good current record - he's averaging 113 (or thereabouts) for 2011...
I reckon it's one of the great strengths of the current team that they're not relying on a couple of star players - everyone contributes at some point.
Still, they've had success with four bowlers, so they may not want to change that. Assuming Trott is out, that'd mean giving someone (e.g Bopara) who's had chances and failed, or putting a new player in, such as James Taylor. Personally, I'd still put Tremlett in, as he's got the experience and the track record, and it'd be a bit of a pisser to drop Bresnan for Tremlett after the lad just took 5 wickets.