In China they have lots of new MIPS developments based on existing MIPS architecture.

The question it's not if someone will use some old MIPS ISA in a few years from now on, the question is if someone will improve the ISA from now on, in the same way x86 and ARM are consistently being improved.

Some companies are still fabbing old Z80 CPUs, but that's not to say Z80 has a bright future.

Ingenic an Loongson both have architecture licenses and so far have kept releasing new chips with their own cores on a regular basis, including (in Loongson's case) some interesting enhancements. Both are also members in the RISC-V foundation already though, so it seems likely they would in the long run pivot their instruction sets to that, like others have done before them: Andes, C-Sky, Cortus, Cobham-Gaisler, NVIDIA, and presumably many more all keep supporting old products based on their previous designs while doing new development on RISC-V.

CIP-United still promises to provide enhanced versions of the both the architecture and the MIPS Warrior cores for the Chinese market, regardless of what happens to MIPS Technologies. This may seem utterly futile now, but it is also the very thing that the US Committee on Foreign Investment was trying to prevent when it required MIPS to be spun out of Imagination Technologies when that got sold to Chinese investors.

Hardly. It means the IP will be sold off to someone else, who might just make it more expensive to milk some profit from the deal while pushing customers to their own platform.

I was under the impression what MIPS was open sourced, in which case "owner" company should be irrelevant?

Not so; there was a short-lived initiative to work towards some kind of open release, but it came to nothing. The article mentions that.