Using Rom Manager was a mistake, but probably wouldn't brick your phone. It just doesn't play nice with the S2, tends to cause bootloops & break recovery.
If the phone won't boot at all, no download mode, no recovery - your only option is service centre or local mobile repair shop. Nothing you can do to fix it.
I mean, try a jig by all means, but understand this is very unlikely to get you into download mode.
Having said that, you need to be 100% sure you can't get into download mode (power/home/vol down), if it was me in your situation, I'd be trying over & over & over given the alternative.