Schooling fish school to reduce the chance of any one fish being eaten, so when there's fewer schooling fish of the same species, they will be more scared of being eaten, and will probably tend to hide more. They also seem to lose a lot of thier colour ( a sign of stress if I'm not mistaken) when there reduced to a single fish in my expierience.
Really the fact remains that if you don't want your silvertips, or don't want to maintain the school anymore, you can always find them a new home. However, I would prefer if you kept the fish and maintained the schoools, in order to insure there properly kept and not introduced to a death trap with no water changes or a stupid person who decides to put a 6 inch oscar in the tank with them.
On a side note, they will survive with an insufiecient school size, but the quality of life will really diminish.