To suddenly confine a cat which has been used to unlimited outside access can be hard, but it can also work if you put the ground work in. Invest in lots of toys, think about the need for stimulation and the need to burn off energy. They will also need extra time spent with them. In general cats which are left for long hours on their own can get into trouble. So interactive things will be good. Have you tried Da Bird (available from the Purrs shop.)? Think about the dietry aspect as well. Cats often eat a blade or two of grass to aid digestion so a tray of cat grass may need to be provided... or you can buys biscuits which have the added nutrients.
If you do decide to allow puss some outside time, make sure it's always with your supervision at first. Maybe use a harness to begin with?
From experience of rescue (which I've been doing a long time now) a cat which fails to adapt to an indoor only life after outside access is perhaps the most heart breaking. Especially with cats who develop an illness or disability and need to be kept in for safety reasons. Such cats can end up PTS for their own sake as they can suffer mentally and the quality of life become intolerable.
So it's hard to know what to advice without knowing your puss's character, the dangers of your area and what obstacles you now have...other than whatever you do, think of the cat first rather than a sense of loyalty which may be too emotional and not founded in common sense. It may be that rehoming is the correct route for puss's future happiness and long term security so you do need to concider this option as a possibility if things don't work.
I would say if you do decide to go with the rehoming route, please go for a good rescue who will carry out all the necessary home checks and apply a minimum standard of care. Please don't resort to Free Ads as I really would worry about where puss may end up.