Nick Bosa's brother Joey is from the same place (Ft. Lauderdale, FL), and he had no problem staying on the West Coast even when the Chargers weren't all that good. Neither Joey Bosa nor Nick Bosa had any problem going to college in Ohio, 1100 miles from their hometown. The Chargers made the playoffs just once before Joey Bosa signed his contract extension, and the extension followed a 5-11 season that came after the one time the Chargers made the playoffs (as a wildcard at 12-4) during Joey Bosa's rookie contract.
I dislike the Gold Diggers and wish them much losing, but I don't see any reason to think Nick Bosa will "more than likely either bounce in free agency or demand a trade." I'd love to see him leave the NFC West, but I haven't seen him expressing any unhappiness with the Gold Diggers. Is there any actual evidence to suggest Nick Bosa might want out of Santa Clara?
Also, as much as I dislike the Gold Diggers, I disagree with the statement that "[t]he only thing really going for the 49ers is their coach." First, I think Shanahan II is overrated. Second, the Diggers have a pretty strong team and while they're short on cap space right now, getting rid of Garoppolo would solve that problem, and they're in relatively good shape for the 2023 cap, and could make that situation even better with well-structured extensions for players like Nick Bosa. I'd very much like for the Gold Diggers to sink into irrelevance, but I also think we have to respect strong rivals, especially at a time when our own team is not considered strong.
Please note that I said Little Shanahan is "overrated," not "bad." He's gotten the team to the NFCCG twice and the Super Bowl once, and he even got them out to a ten-point lead in the Super Bowl with 17:35 remaining. That lead was still ten points until it became a three-point lead with 6:13 remaining. So the Diggers and their coach have gotten very close to winning a Super Bowl. The little guy under the big cap is not a bad coach (tho' he has his flaws), and the team still has a contender-worthy roster.