I think I will sell everything I have (btc and alts) in the end of december, to USDT.
1) transfer it (usdt) on Tron on my ledger
2) Wait months
3) Wait again
4) buy back when bloodbath looks over
5) triple my holdings
No need for that plan to take effect in December.
We don't know what will be the trend for that month. You can actually take effect and deploy that plan now as we speak.
For a test strategy, you can have some small trades starting now and see what will be the result.
Main question about my plan is it safe or not keeping usdt for months?
Although there are lots of raises and concerns regarding USDT, it's not that they will be busted right away. You can keep it on USDT if you preferred it but always be updated on it.