Bear markets are usually seen as Bitcoin-only market. As a dump for Bitcoin means a big dump for alts and a sideways movement also means a dump for altcoins. As many investors try to get their money out of alts and but it into the “less” riskier Bitcoin. But this does not mean that there won’t be any altcoin survivors.
There will be a bunch of altcoins that will “survive” this bear market if we talk in the sense of not being completly irrelevant afterwards. But in general something like 95% of alts likely won’t be as strong again as they were once before.That’s why buying Alts during a bear market is like going on a field with landmines everywhere. The probability for you to lose your money is definitely at ~90%, that’s how it has been in the previous bear runs.
Without Alts obviously Bitcoin would not exist like that and Alts offer the most return in comparison to Bitcoin but you should be extra careful while buying alts in a bear market and be prepared to lose your whole investment in the worst case.