The two helos that I know of that have (had) ejection seats are the Kamov KA-50 coaxial and the Sikorsky experimental S-72 RSRA (which was also the DARPA X-Wing).
They both have elaborate mechanisms to blow off the rotor blades and they use extractor rockets with thether ropes so the G forces on ejection are low.
Frankly, the weight, cost and maintenance burden of blade removal/ejection (as well as the depression it will cause in your passengers) makes them poor bets in any helicopter that I want to fly.