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).
Best Answer
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.