Quote from Let My Nation Live by Yosef Deustch, based on aggadata and many commentaries from Ibn Ezra, to Chasam Sofer:
Acheshverosh, however, enjoyed a great improvement in his situation.
His appointment of Mordechai as prime minister also enhanced his
position greatly. He regained all the lands he had lost to the
rebellion in the early years of his reign and even gained some lands
and islands he had never before controlled. His opposition to the
reconstruction of the Beis Hamikdash had caused the downturn in his
fortunes, but now that he had been kind to Esther, Mordechai and the
Jewish people, Hashem restored his losses. Furthermore, Hashem honors
the Jewish people by elevating the kings who rule over them.
More secure than ever in his power, Achashverosh reinstated the taxes
he had suspended in honor of Esther becoming queen. In fact, he raised
the taxes even higher than they had been before to punish the
provinces for not speaking out against Haman's injustice against the
Jews and to replenish the imperial treasuries, which had long been
deprived of the revenues. No longer would anyone be exempt from taxes,
not even high palace officials and dignitaries. Cemetery taxes were
instituted and made mandatory; with all the deaths this was a great
source of revenue for the king. So great was his power that even
nations outside his empire paid him annual tribute. Once again,
everyone under Achashverosh's rule was impoverished by the large taxes
they had to pay.
The only exception was the Jews, who now got a tax exemption for the
first time. Achashverosh considered it only fair that the Jews, who
had paid taxes for seven years while everyone else had not, should get
a respite of their own....
...In the end, Mordechai did not serve as prime minister for very
long. Achashverosh's entire reign only lasted fourteen years. He died
young, in retribution for having stopped the construction of the Beis
Hamikdash and the torment to which he had subjected the Jews, but he
did gain a share in the world to come by emerging as their champion
As you can see, he was punished with an early death due to his wickedness, but was rewarded with prosperity in his later years, and Olam Haba, for his change of heart in the end and emergence as the Jew's protector.