He had lots of things to say, so he won’t seem to end his talk soon.は厳密にいえば、文法として間違っていると思います。(通じますが、正しくはない)
He had lots of things to say→過去形
so he won’t seem to end his talk soon→今の話？
ですので、あまり深く考えなくて良いかもしれません。
正しい文の例は下記です。
He has lots to say, so his talk seems to not be ending anytime soon.
間違えました。He had ???? He has です。
Tim