Advice would be to get that flexibility back ASAP. It was extremely painful, but worth it.
I set up a road bike on a trainer in my living room and raised the seat as far up as I could. Then I'd pedal until it didn't hurt as much. I'd lower the seat an inch at a time and keep doing that until I couldn't anymore. I wasn't putting weight on it: My bike shoes clip on so I'd pedal with my left leg and my surgery leg would be going along for the ride.
I got to 90 degrees and further on a pretty tight schedule which was great.