Having made the decision I second-guessed myself and have done so ever since.  But there wasn't any perfect information, it was what I did.  I found a flight going to Shanghai via Phuket a few days later and booked it.  

I had used a bit of calculus modeling to predict when to book the flight based on the current exponential take-off of covid cases in Thailand and the situation in China with when they would successfully contain the first wave.  If you're interested, it was mainly based off the standard S.I.R. Model.  My employer at the time thought I was a sheer genius for using calculus to do something like this, and he tells the story ever since.  To be honest it was a bit of brains but mostly luck as these mathematical models are far from perfect.  They don't account for freak events such as super-spreader events or other types of chaos we find in the real world.

But with the flight booked, I then did a bike ride around Chiang Mai to secure necessary items for a survival guide

1.  New backpack to fit in all the electronics and keep the clothes in the old one, so as to make everything neat and organized, ready to be disinfected.

2.  A bunch of snacks and bread to tide over 8-12 hour waits or even longer at the Pudong airport on arrival.

3.  A large assortment of proper face masks.

4.  Battery packs fully charged to keep the smartphone running

5.  An electronic copy of the police registration of my address in Shanghai

6.  Abundant money loaded onto the 4G SIM card of my Shanghai number that I had smartly kept in my phone the entire time with its dual-SIM holder.  

7.  A detailed list of my travel history, combined with proof in my passport to show I had traveled through low-risk areas.

[Update November 2022]  The only thing I had forgotten was the old Thai SIM card which was a huge blow as it had all my old social media contacts and chat histories from the friends I had made on this trip.

My fiancee back in Shanghai was overjoyed that I was going ahead with this trip and she was ready to help in any way.  

So, checklist done, plan in hand, it was now time to do only one thing:  execute it.