There is zero guarantee of any new product coming. Whether any product. We know Apple has a big event planned next week. And we know products will be announced. If they announce an M5 Air, then if you are in your 14 day return period, you can return and get the new model instead which I would do. But the difference between M4 & M5 depends on what you do daily on your Mac. Or your needs.
For all we know maybe because of the RAM crisis and everything else, the M4 MBA sticks around for a while and next week only the M5 Pro & Max MBP and budget macBook get announced outside of iPhone 17e and new iPads. Maybe no iPads. We don't know. You buy for now not worrying about what is to come. And again if you are in that 14 days return period and something does come out then you are covered. And Apple does work with people at the stores also, I have seen very nice employees and managers help people.
All we can do is see what is announced this week, people assume this this or that but Apple has surprised people in the past and I personally don't see 5+ Macs being released next week between the budget macBook (pretty much guaranteed), a 13" and 15" MBA M5 and and 14 inch & 16" MBP M5 Pro & M5 Max models. Plus new iPhone, plus iPads. Just seems too much for one week based on past patterns.