A lot of people don't bother with starters on dry yeast, but I always keep a couple of packets of some decent yeast (Nottingham, Coopers Ale, Safeale 56, & Champagne) for the times when I just feel like experimenting with recipes. Once I get the itch, I just re-hydrate and pitch to a starter. It usually takes me a day or two to get all my gear together from the basement up to the brewhouse (garage) in between work and keeping the boys from killing each other, so that works out perfectly to have a good batch of pitchable yeast by the time I'm ready to go.
Dried yeast is fairly tough. A 11 gm packet starts with about 100 billion cells and if hydrated and used optimally, just about all of them will be viable. The worst case, pitching to chilled wort and stirring, will kill about 40%. This will add 2-4 hours to the growth phase (AKA lag time) before fermentation starts.