Nothing will really change unless Powers regularly attack each other. While this attack is impressive, attacks like this have been done in the past and not followed up so I expect those 34 systems will slowly drift back to Mahon.
The next test will be if anyone opposes Mahons inevitable expansions again.
The Imperial HQs haven't gotten any closer to Gateway in the last six years. I have no idea what's dropped, but if this case is anything like the last time Mahon saw systems revolt, I imagine there are no options worthwhile for Patreus or ALD. Torval may have one or two possibilities, and Aisling may be willing to stretch their haulers 200 LY to pick up CC.