I am 46 w/ddd, prob from ra. pain fluctuates, but always numbness/pain/cold in legs. dr wants to fuse s1- l4. if i don't, what are likely consequences?

DDD is not RA: First, RA does not affect the lumbar spine to a significant degree. Cervical spine, yes. Lumbar, no. Consequences of not fusing is dependent on reason for fusion. If fusion elective, then only consequence would be continued pain. Not likely a risk of paralysis or death without surgery.

Most likely remain: With the same symptoms but also a possibility of improvement with time as the degeneration is your body's attempt to correct a situation which does occur. There is also a chance that your symptoms may worsen but that does not prevent you from treatment in the future.