No, I don’t think so. The only non-liberal Lutheranism that I know of is Missouri and Wisconsin Synod that might number about 2.5 million combined.
And Luther was no theological liberal.
So, numbers mean what?
What percentage of the world’s population was Palestine in 30 A.D.? And then what percentage of Palestine’s population followed the Christ? The numbers were pretty small. That’s one way to answer you and your assumptions.
Another way to answer would be ask how many “Lutherans” are there in the Catholic church and the Orthodox church and in the various Protestant brands? More than most people think.
Finally, Lutheranism, or more properly put, adherence to the faith confessed in the Book of Concord (which begins with, and is founded on, the three ecumenical creeds), is not a church. It is a confession. It never made any pretense of being more than that. There is but one holy Catholic/Christian Church. Entry to it is afforded by faith. Its numbers are known to God alone.
Lutherans serious about their faith (and you are right, this would not include the clergy of, for example, the ELCA) are not too worried about numbers. That, they understand, is pretty much in God’s hands. Their concern is faithful confession of the Triune God into whose name all Christians are baptized and of Jesus Christ in whom alone there is forgiveness, life, and salvation.
So, no, I don’t think Lutherans are anywhere near as close to extinction as some would like to imagine.