I know I posted a more general question about this in the "Concepts" section...but, specifically about grappling... I've had to stop my grappling training, as well as all training in other styles, due to unexpected circumstances.
Grappling is probably what I'm best at, and I REALLY hate the idea of losing what I've learned in these past three+ years if I can't continue practicing in the near or perhaps even distant future.

Will what I learn in other sports and physical activities add to my mental and physical abilities to grapple, or will I gradually lose what I've learned?

Once a grappler always a grappler?

Something like that has happened with me. I can no longer wrestle or practice "heavy" grappling styles, but occasionally have to tangle with people. The skills are still there, but I would get stomped by people I used to fight even with.

I took up Tai Chi, then later Xingyi and Bagua with people who are aware of my limitations. I wish I could go back and learn some things like BJJ, but I can't. Over time I,ve gotten more enthusiastic about these other fighting methods, which I see as primarily standing grappling methods.

Have you looked into "soft rolling"?

Me too...grappler forever!

i see this one black belt who is a senior, he even does rondori with the young people...

doing a forms based CMA would be just as hard I would think on the joints as doing judo or bjj. Judo is a hard sport, and at the club that I train in there are a lot of older fighters (35-55 yrs old) that spar pretty hard with younger men 15-25. However, many of the senior fighters tend to have an advantage in weight and training experience, which tends to even things out a lot.

I've broken 17 bones since 1998; for example, a "sore low back" from Aikido turned out to be spinal compression fractures. Soreness I can accept, even the occasional broken bone, but one of these days something that breaks will be something I need and can't get fixed. I get away with a lot, but I've got to cut my risks. For me, the best way seems to be to train internal arts. One of the local IMA clubs puts on MMA gloves and armor and goes at it full contact weekly. They WILL fight better than me. I don't fight with conditioned athletes, though. The street fighters I tangle with routinely aren't real fighters, and go down in seconds (shooting Heroin and Cocaine "speedballs" doesn't seem to turn you into a skilled fighter).

yuck, i wouldnt even want to touch a guy like that, let alone make him bleed.