I think that if there is no alt coins then the exchanges will have less profit.
Bitcoin will rise too much (much more that it is now) and early investors will be happy
Most of the altcoins are secondary compared to bitcoin. I consider none of them a real treat to bitcoin. Not by a long shot anyway. So without altcoins bitcoin would have probably done the same.
there is never a "threat" for bitcoin even if there is or will be a good altcoin out there that can compete with bitcoin, it will only be a competition at best.
I honestly don't see any reason why bitcoin can ever be threatened or be replaced, because even if a new altcoin is created with fantastic features that can become better than bitcoin it will only be an alternative way of using crypto currencies and will be used alongside with bitcoin.