If I write
If $x \rightarrow y$, then $y \rightarrow z$.
it looks fine. But if the sentence is more involved and formulas longer, I tend to change
\[...\]. In many cases I think the result is ok, especially if there's only one equation in the end of the sentence.
However, in the above example it would be like:
The comma and period doesn't look very nice.
Sure, I could break it up and say If formula (1) holds, then formula (2) holds, but this is usually an overkill in my opinion.
TL;DR: What do you do with periods after sentences ending with a