Survival rate with systemic mastocytosis?

Normal: Unless there is an anaphylactoid reaction there should be a normal life span.

Usually normal: Most people with a systemic mastocytosis have the 'indolent' variey, in which case their life span is the same as anyone else's (provided they get appropriate treatment for any anaphylactic reactions). There are very rare cases that we call 'aggressive.' in this case, it may shorten expected lifespan depending on just how 'aggressive' it is, but some of these may be amenable to treatment.