No it's not shrinking just yet although they clearly don't see Windows as a cash cow like you are suggesting. Their moat is in having diversified but complementary business units.

Microsoft made $21bn on $90bn in revenues [1] and the stock market responded by sending the stock to an all-time high of ~$74 [2].

Microsoft is still a very healthy business and will remain so for a while.

[1] https://www.recode.net/2017/7/21/16008618/microsoft-all-time...

[2] https://www.google.com/finance?cid=358464