https://spimsimulator.sourceforge.net/
RISC-V looks a lot more like MIPS than it does RISC-I to IV, so on the technical side having MIPS-the-company abandon MIPS-the-architecture was not such a huge change. And DLX that the Hennessy and Patterson books used before they were changed to RISC-V was essentially MIPS as well.
The ISA and its implementation are two different dimensions. Look at the x86 ISA how it evolved from 80386 to present day superscalar, predictive, re-ordered, who knows what else microprogrammed implementations. The code I compiled back in 1990 runs today without even recompiling it. My sleek light-weight laptop is totally unlike the beige box I originally compiled it on.
https://en.wikipedia.org/wiki/MIPS_Technologies#Notable_Cont...
In either case, I am not aware of any of them being RISC-V leaders though John Hennessy did rewrite the books he co-authored from DLX to RISC-V.