Things will change: idiom or proverb

Is there an idiom or maybe a proverb stating that things will not be the same or as you want, forever.
For example when telling someone that they might be in a good state or status now, but they will sure some day face difficulty or trouble (when they, for instance, feel so certain that they won't) more like warning, threatening or something.

A: He always bosses us around. We're really tired of that.
B: I know what you mean. He will face the consequences some day. Things will not always be as he wants (something to replace the last sentence in italic).

This too shall pass. It's appropriate both for the impermanence of good things and bad --there's a fable that a king asked his wise men to give him something that would cheer him up when he was sad, humble him when he was proud, comfort him when he was mournful, and calm him when he was agitated. After much deliberation, they gave him a ring with those four words engraved upon it.

For your particular use case, there's also the saying "the bigger they are, the harder they fall," which is specifically used for predicting the downfall of the high and mighty.

You could consider using what goes around(,) comes around which means:

Prov. The results of things that one has done will someday have an effect on the person who started the events:

'So he finally gets to see the results of his activities. What goes around, comes around. Now he is the victim of his own policies. Whatever goes around comes around.'

[McGraw-Hill Dictionary of American Idioms and Phrasal Verbs]

I think the Wiktionary has a better definition:

A person's actions, whether good or bad, will often have consequences for that person.

The Buddha's last words were

All conditioned things are impermanent.

If you want to convey that things are good right now but will not be good forever, you might go with:

• All good things must come to an end.

or

• Happiness is fleeting.

In your specific context the second works better, as in "Things will not always be as he wants. Happiness, after all, is fleeting." Or you can just replace italicized sentence with the latter. But it may not be fully satisfying in that context.