If my SSDI is cut off, will my Medicare end? What if it gets reinstated?

I’m going to receive a letter by the end of month about my SSDI being terminated(?), since I didn’t send in the monthly paystubs when I had a part-time job. I had the job for the past 3 years or so, and it ended in June. I haven’t been working since. I was always under the SGA, but I did pass the 9-month Trial Work Period.

My work health insurance will end 10/31. I had planned to start a Medicare Advantage Plan beginning 11/1. I planned to also get Part B again so I can get Medicare Advantage; I currently just have Part A. (I’ve had Part B in the past, and I cancelled that when I got my work insurance. I’m under 65 with a disability, but I can use the same Medicare Advantage plans as seniors who are over 65.)

If my SSDI is cut off, will my Medicare end? I’ll try to get my SSDI reinstated; if that happens, will my Medicare be reinstated as well? How long does that take? Will there be a period when I don’t have Medicare at all, and can’t get Medicare Advantage? What do I do about health insurance in the mean time? What do I do in my case?