An offer is possibly quite far from buying. It seems there may be multiple offers. All could be refused.
At minimum it does help set a base valuation for the next funding round, if there is one.
I struggle to see how such a deal would make sense for anyone. Ok, maybe SiFive founders if they want a "never need to work again" pay day now rather than a potentially much bigger pay day later on. But I think at least Krste, Andrew, and Yunsup actually do want to change the world and burying SiFive inside Intel quite likely would not help with that.
Intel doesn't need to buy SiFive to get a license to make RISC-V chips. Anyone is allowed to. Buying SiFive doesn't give control of RISC-V. Intel doesn't need SiFive technology, unless they're planning to get into microcontrollers and IoT, and even then they can (and already do) simply license cores from SiFive. SiFive's most sophisticated shipping cores are around original Pentium or PowerPC 601/603 in complexity (at much higher MHz obviously) Pentium Pro level cores have been announced but are not yet shipping. That's 25 years behind Intel. Intel could do an Apple M1-style RISC-V very easily if they want to, but they don't need to buy SiFive to do it -- it wouldn't even make it easier, particularly.
Does it make sense for SiFive or RISC-V? It's hard to see it. Too much risk of getting buried inside the behemoth. It's not even as if Intel can threaten to compete with them and squash them -- SiFive's battle for the foreseeable future is with ARM, not x86, and not an M1-level RISC-V (if Intel wants to make one)