Irene didn't die or be jailed in the original; she left & lived a free life on 'the Continent'.
So there was no need to have her either jailed or dead in this adaptation; they stuck to the canon & allowed her to live.
She never made another appearance, but she was mentioned in passing in 3 other stories. So while the door is open , there's no necessity to bring her back.
I daresay the next series will bring an equally brilliant adversary for Sherlock, possibly just as or more tantalising in some way to those we have seen already. I don't doubt Moftiss's abilities in that area. Then fans will be asking for THAT one to come back, and on it goes.
I enjoyed Moriarty & Adler but I hope for something different next time.
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Also, please note that sentences can also end in full stops. The exclamation mark can be overused.
Sherlock Holmes 28 March 13:08
Mycroft’s popularity doesn’t surprise me at all. He is, after all, incredibly beautiful, clever and well-dressed. And beautiful. Did I mention that?
--Mark Gatiss
"I know that you believe you understand what you think I said, but I’m not sure you realize that what you heard is not what I meant."
Robert McCloskey