Let’s read about “the God of the living” in context:
Matthew 22 (NKJV)
As you can see, Jesus said these words about God being the God of the living in response to the Sadducees who believed there was no resurrection. He prefixed this statement with the words “But concerning the resurrection of the dead…” If you believe the words of Jesus that He will raise the dead on the last day, then in uttering the words, “God is not the God of the dead, but of the living,” Jesus must have been referring to Him being the God of the living after they would be raised to life again.
However, maybe you think the resurrection is past already, as Hymenaeus and Philetus taught in Paul’s day, and against whom Paul warned . Those who hold that belief, also hold that when a person dies they immediately go to heaven and that is their resurrection.
Paul’s statement does not imply that he was saying that he would be with Christ immediately upon his departure, but that as far as Paul personally was concerned, it would be immediate—and so with the rest of us. Perhaps after your death and you find yourself immediately with the Lord, if you see me, you might say, “See, Don, I was right. We went directly into the next life to be with Christ!” You would be totally unaware of a possible time span of 1000 years or more between your death and resurrection.
I experienced a bit of that when I received prostate surgery in 2007. I was lying on a hospital bed and glanced at the clock. It was 1 P.M. Then I thought I heard a little tinkling sound. I glanced at the clock again; it was 3:30. Two and a half hours has passed with the surgery complete. But from my point of view, NOTHING had occurred between 1:00 and 3:30. I went instantaneously from my state at 1 o’clock to my state at 3:30.