I wasn't able to get a firm time from the Chat support as to when the name servers would be back up. Like you mentioned, both ns1.dynadot.com and ns2.dynadot.com name servers were not responding.
I've since changed two of my domain's name servers from Dynadot's custom DNS settings to instead point to a different name server instead. First write down i.e. copy/paste any settings if you use their custom DNS Settings so that you have them - a screenshot also helps although may cutoff important info. Highlighting all in each field then copy/pasting seems the safest - ensure you write down the correct type of record (A record, CNAME, TXT etc).
Then re-setup on a different name server hosting provider and re-enter all your settings. Then point your domain's name servers over to the new name servers.