If anything mechanically fails on your brand new bike, "due to inferioir parts or workmanship", in the first 2 years, other than wear and tear items like clutch cables, brake pads, chain wear or tyres... (or maybe having a rock crack open your engine block) you're covered under warranty. Unless the dealer can show that you were playing around and broke it in the process, or you did something contra the routine home maintainance schedule like draining all the oil out and then riding it around.
Try checking here
http://www.triumph.co.uk/media/warranty_English.pdf
I think the rule of thumb that a lot of guys are working to (at least in my case) is, if it's a quick fix, or just a minor adjustment... do it yourself rather than lose half a day trawling all the way in to a dealer, having to make your way home without the bike, and then lose the bike for two more days whilst they tighten two loose bolts. :-)
If in doubt, just call your dealer before you tinker.
If it's gonna cost me money, or involves anything other than basic adjustments, I'll take it to the dealer. After all, that's why you pay a premium (in depreciation) for having a new bike.
As for your service being 250 miles over....
Tsssk Tsssk Tsssk... Your stuffed now... Warranty void... It's on page 14 of the manual... In small print... In Egytptian heiroglyphs...
Joking. You should be fine taking her in after 750 miles, most dealers seem to think that a service after 500 miles is too soon anyway.
Enjoy.