Well, first of all, Melo has a no-trade clause, so he could easily just say no to any trade if he doesn't want to leave NY. But, even if he is willing to accept a trade, it likely only going to be for a few select destinations.
What would be silly, would be to trade away your franchise superstar for pennies on the dollar, which is what teams would likely offer, without ever even trying to rebuild around him. It's also silly to act like being 30 is some sort of death sentence. Melo is still a highly productive player.
If in a year or two, it appears the Knicks are still going nowhere, I would expect the Knicks to seriously look a trading Melo, though. And i'd be willing to bet the offers wouldn't likely be much different.