“The Constitution clearly says the legislatures have the sole right to appoint electors.”
No, it says they have the power to determine the manner in which those electors are appointed.
If the process is not followed, what happens? Do they have a fallback provision?
In 2004, the Florida legislature was preparing to intervene and name a slate of electors when the Supreme Court ruled against Gore in the selective recount.
I am not aware of a specific case on this topic, but I believe the USSC would be hard pressed to overturn a legislative vote on it.
As I now read the statute (and talk with legislators), it will be challenging for the legislature to act. The 1937 statute would require those counties in question to have a judicial resolution PRIOR to being certified by the PA SOS.
If they are certified, the votes count and the electors get named.
Others from PA with more detailed knowledge are welcome to contribute. The message I received was..stay tuned.