In the same vein it is natural to assume that the death of the altcoin world would eventually do only good to Bitcoin in the long run as people won't be losing money anymore. So what d'ya think?
This would depend on whether the cause on which most altcoins disappeared has something to do with the market or prohibitions caused by third-parties (e.g. government, etc.).
If the cause of disappearance has something to do with a prohibition executed by counties in disallowing the utilization of alternate coins in general, then expect that this may also affect bitcoin negatively.
On the other hand, if the cause of disappearance of altcoins has something to do with the shift of the investor's interest in the market and they are leaning towards investing MORE in bitcoin, then this may affect bitcoin in its price positively. This would entirely depend on the reason on why altcoins are slowly dying on the market.