if you need to drop 50lbs then you need to be hitting the weights...go find classes, lots of ways to maintain lean mass besides a grueling heavy lift session. every single city got some bootcamp/functional fitness spot (not crossfit). you'll likely have to pay $100-200/month for these spots, but if it's what keeps you on track and keeps you from hating the gym, it's worth it
edit: and diet is what's going to make results come...at 50lbs overweight you likely have plenty of muscle on you even if you never added to it. once you start getting the pounds off, you'll start seeing it. of course to maintain what you have you need to workout, that's why i'm suggesting classes, you don't have to always go heavy and shyt like people really pushing for mass/strength. plus having people/coaches who know you starts keeping you accountable and you look forward to your workouts