The thing that indie devs don't recognize about gaming is that it's a hits business, just like film and music. _Success of your franchise is not an endorsement_. People consume hits and toss them away for the next big thing all the time. The reasons independent game companies make these mistakes is that they conflate the mass appeal of their creation with a personal endorsement and assume anything they do in the future will be well-received. That's rarely the case.
To be a successful player in the hits business, you have to be putting out new, formulaic stuff constantly, aware that some percentage of it will never make back its money, some may break even, and some will make a lot of money. This is what movie studios, record companies, and the successful game conglomerates do. As much as it may get tiresome to see the bi-annual CoD release break records, it matches the expected behavior perfectly.
But I digress. The direct answer to your question is pretty similar to what it always is: don't grow too fast, don't let it go to your head, and diversify. Personally, if I was in that situation, I think selling out to Activision or EA, who already have a functional hits apparatus, would be a path warranting serious consideration. A lot of game developers are eventually forced into that position anyway after they make the erroneous assumptions discussed in this comment and become financially distressed.