If elon musk (or any far-right billionaire) bought Reddit, do you think there will be a mass exodus to alternatives like Lemmy, similar to the twitter exodus to Bluesky?

There will only be an exodus if there is a better alternative than Lemmy/kbin. Remember that twitter was still going strong despite mastodon existing until bluesky won the race and became the new twitter. If reddit somehow manages to collapse one day, most of the people won't go to lemmy because it's already been shown it's not an attractive or equivalent replacement for it, so either something new reddit-like appears or nothing changes.