I'm familiar with the experience of readers begging for a sequel. Instead I try to satisfy them with my other new stories. The story in question has a very final ending, by design due to plot reasons, and a sequel would be very difficult. Not that I haven't thought about it, but the main concepts that could conceivably be used for a sequel haven't gone anywhere for me, I have set-ups with no rest of the story. Rather than force it I'm just leaving it be.
When I started, I had a 2 series serial planned out ahead of time. I had the various plot markers planned out, but few particulars. My main storytelling technique was to think up interesting characters and toss them in front of my main character, then recording what he did. However, that 2 book (one largely written and one unwritten) went to 3, then 4 and finally 6. I always had the ending in mind, and kept revising the epilogue as a guide, but I didn't have the specifics of the ending (how the MC died) until the final book. I knew he was going to die, I just didn't know how.
However, I've always aim for the ending. Part of that, is that the story ends with little change for a continuation (i.e. the MC either dies, disappears or changes careers). I just tried a continuation featuring new characters, and it didn't work as well as I'd hoped. :(
I guess it comes down to 'enclosed' or 'open' stories. Those who write 'enclosed' stories know how the story will end, and write to that ending. Those who write open stories write to continue the tale, and never know how it'll end until the write "The End".