It seems like you might be well served with a 2 prong approach:
1. Obtain or downgrade to a no annual fee card that will keep your MR alive. Use it sparingly so your account isn't closed. If you qualify, the Blue Business Plus card seems like a good option but there are consumer cards too. Most won't let you transfer your MR to miles but it seems likely that you could upgrade to or apply for such a card when you're ready to travel.
2. Get a different card for primary spending that meets your needs/goals, perhaps a cashback card as you mention.