Changing servers, want to make sure Googlemail doesn't go down

2 things.

1. The TXT record is in fact an SPF record, stating that the two IPv4 addresses 84.45.57.143 and 84.45.57.142, as well as the A record for the domain itself, are allowed sender hosts. Validation of all email from any other hosts with your sender domain, should result in SoftFail (meaning "probably"/"possibly" SPAM). So if you plan to migrate a mail solution from the old server(s), you definitely want to update this.

2. You might want to check with google if you need to go through the domain verification process again, I think that's what the google45673f3fa15785f3 record has been used for earlier. I don't think you need to do this when you move to a new Name Server, but better safe than sorry