I think they will be okay. Your hatch might be delayed a little bit and technically there are some other complications that can happen from low temps late in incubation but honestly, I think they will be fine!!
This happened in one of my brinsea mini's. The temp totally plummeted on day 21 in the middle of hatch! Thankfully I had another one that I could squeeze them all into. I called brinsea and it was covered under warranty. I shipped it into them and about 2 weeks later they shipped it back all fixed up.