Water Heaters - Split System Questions

I currently have a split water heater system in my 2200 SF home utilizing one 40 gallon tank, supplying 1/2 the house and one 50 gallon tank supplying the other 1/2. Our children have finally flew the nest and I was thinking of replumbing the two heaters so only one is required to supply the whole house. I don't need 90 gallons of water for only 2 people. I was thinking of installing 2 outlet valves and a connector tube with a valve between the two systems to accomplish this.

Are there any watchouts that I need to be aware of?

The gas to the unused tank will be shut off, should I drain the tank, or leave it full?

Any help would be appreciated

if the heaters are next to each other you can do pretty much anything you want. just need to disconnect one heater and run the outlet (hot) pipe to the other heaters oulet pipe and then cap the inlet (cold) pipe. it should have a valve but i would not risk having an open ended valve especially in the house. you could also just add a tee and a valve at the top of the heater you arent going to use. the hot water from the othe heater needs to be blocked from entering the obsolete heater

if you are going to keep the 40 gal heater as an emergency heater i would keep water in it otherwise the tank will rust and you dont want that. just make sure to drain and refill it when/if you decide to put it back in service