When President Obama chose my senator, Hillary Clinton, as Secretary of State, Governor Paterson appointed my congresswoman, Kirsten Gillibrand, to replace her as senator. So here in NY-20 we had a Special Election to replace her - sticks in my mind since I worked on that campaign. So wouldn't the Massachusetts governor appoint a replacement for Senator Warren? I remembered that this is a concern since he is a Republican.

Frank Lautenberg died on 6/2013.
Governor Chris Christie appointed a Republican Jeffrey Chiesa to that seat.
Chiesa declined to be a candidate for the 2013 special election.
Cory Booker won the special election.

Joe Kennedy 3rd is favored to win in the general over whoever the Republican Nominee is assuming Kennedy 3rd does not behave like Martha Coakley who lost the 2010 special general election to replace Ted Kennedy.

I guess the difference was that since Gillibrand was appointed by the governor, they waited until November to hold the Special Election. The election to fill her congressional seat was held immediately - in April of 2009. I worked on that campaign and the succeeding one - for local (to me) candidate Scott Murphy.

And I agree that young Joe is likely to win - he's bound to be popular, just not as popular as incumbent Ed Markey.

The Republican Governor would appoint until the special election

and am considering this:

https://www.google.com/amp/s/www.boston.com/news/politics/2020/09/01/joe-kennedy-ayanna-pressley-senate/amp