A wee while ago, DealZone posited that bonus-hungry bankers who had gravitated to bank prop desks might return to the once-glorified M&A desks after the Obama administration targeted banks’ proprietary trading as a business too risky for banks. A logical argument, but one that ignored an aspect of the M&A game that is becoming starkly obvious: deals putting trading operations into banks are clearly at risk.

A source tells us that JPMorgan is rethinking its planned $4 billion purchase of RBS Sempra with an eye to let the U.S. power and gas businesses be bought by Sempra Energy, which jointly owns RBS Sempra with Royal Bank of Scotland. This would leave the U.S. bank with the joint venture’s oil operations and all of the non-U.S. businesses, a source familiar with the matter said.

JPMorgan started exclusive talks with RBS and Sempra on about Jan. 20, after warding off rival suitor Deutsche Bank, which is not expected to have re-entered any talks, according to sources familiar with the situation. But if U.S. banks wind up having to chop and trim their own deals to conform with new regulations, European and Asian rivals may well wind up picking up high-octane U.S. trading assets.

Of course, a multiplicity of smaller deals could in the end be as good news for those M&A bankers as a smaller number of megadeals in the commodities banking space.