I've been reading TOS forums since 2004, and I don't think I've ever read about anyone having a stroke due to TOS.

Is there any history of strokes in your family?

A clot "might" be possible, pretty rare, if I recall it is most likely in the area of where the compression is or downstream (arm). You'd probably know if you got one, they hurt, swell and usually make a red area. My sis in law & a niece both had clots, one in the leg & one in arm - theirs weren't TOS related.

about the progression of TOS,
it all depends on what is the root cause - and what if anything is being done to change the cause.
If you are think it is work /postures / hobbies, then some changes need to happen to stop the progression.

Have you seen the self care suggestions and tried any of them?
The passive gentle posture correction/stretches should be good for most of us.
Have you figured out what might be the cause of your TOS?