I might have missed this somewhere, and not trying to be rude, but how old are you? (I admit to not reading most of this thread) I think that would play a huge part in the outcome of your little debacle. You don't have much time left for a full pension, but you still could be in your 40's or in your 70's for all I know. I'm not financial advisor, and up until recently I didn't even have 'fair' credit, lol but here's my take.
You never said how much this 'windfall' was, which is another key item missing. You need to figure out your monthly bills (realistically) and set a monthly budget. How long will the windfall last just paying your bills? If it's 10 years, I'd say you're on the right track. If you got a 'Windfall' of 20 grand, and it'll almost cover you for a year I'd say you're dreaming. Without knowing your bills or your lifestlye, I would simply say that for 5 years I would need at least $300,0000. to say you could retire early. That's $150,000 ($30,000/year bills) and an extra $150,000 ($30,000/year) to maintain the lifestyle.
With that said, Time is always more valuable then money. If your house is paid off, you have no rent, kids, car payments, etc. etc. and you can get by on $300/week or something like that, Then go ahead and do it.
Anyways, enough rambling. The real point I wanted to make is this. You're asking on an internet forum if it's OK to retire early. You need to figure out what your Pension payments would be at this reduced amount. If that's enough to sustain your lifestyle, and this windfall would cover those pension payments in the meantime, then go for it. I've never met a (well off) retired person who wished they would of worked a little longer. Life's too short....But if you have to ask, I'd suspect you're not really ready yet...or looking for attention....