Tyrion and the team should've told Cersei...
That if they fall, they'd all be coming for her (reanimated dead) and in greater number than 100k.
To be fair though, Jon did tell Cersei how to kill the dead by fire or dragon glass (from dragon stone). All she would have to do is have them fight in the north as a delay tactic to mine and amass dragon glass along with lots of fuel for fire. Then again, the dead would have 3 cold fire breathing dragons with them so we're back at that Dany has 3 fire breathing dragons and we couldn't stop them issue.