I think bitcoin would be the same and would maintain it's popularity without altcoins and wouldn't have that much of an impact, The opposite is almost impossible IMO at least how we see it right now since altcoins is still priced mostly just for BTC.
I don't think so because without altcoins bitcoinwill jot have this popularity, and start from the forum where most of the activity is focused.
some people seem to forget that bitcoin was first created and when it reached a success level alone all these many many different altcoins started to show up out of nowhere.
so even if they disappear bitcoin will still remain and stay string.