Sunset is pretty high up on Inglebough, so its gonna react very quickly to weather - that is water levels will go up and come down pretty fast. However the ground is pretty water logged at the minute, so it'll react to small amounts of rain.
The forecast is a bit iffy for friday night and saturday morning and Inglebough tends to have its own crazy weather system, so its going to be difficult to guess if its gonna be okay or not. Best to keep an eye on things and see whats happening on the morning your planning on going.
Having said that, Sunset is pretty straight forward, so as long as its not raining when you go and you rig the small climbs and run away if its deathy you'll most likely be okay.
I'd most definitely have a back up plan though. For small pitches and weatherproof, Sell Gill is probably your best bet.
B