Could I just delete the Monero GUI wallet and wouldn't it just go back to being cold?
You could delete it and it would become kind of "cold", but if it was "hot" at any moment in time, then during that time you were exposed to the risk of leaking your wallet file / password / mnemonic to some adversary if your computer was compromised at the time you made it hot.
It's all about managing risk. The CLI/GUI wallets are pretty safe even when "hot", and I'm not aware of anyone getting his funds stolen so far. But it's really as safe as your computer so one always needs to be careful! As a minimum, keep your computer clean and up to date with security fixes, have some anti-virus, don't open suspicious links or software, and use a strong password for the wallet. After all, being your own bank also means you have to take responsibility for your security.
So if I ever wanted it to go hot again I would just reinstall the wallet and import the wallet from the seed and sync the chain?
That's right. But bear in mind that anyone could do the same with your mnemonic and steal your funds, so keep it safe!
If you want a compromise, I'd suggest running some "live-CD" Linux to access your wallet, and keep the copy of the blockchain on some USB drive so you don't have to re-sync the blockchain from scratch every time.