No, but also yes. But definitely no. A quick history:
American superhero comics peaked in the 1960s (with Silver Age Superman, who had something like 22 million regular readers in comic books and newspapers.) In the 70s, comics were for young adults and still sold reasonably well. But they were sold on newsstands, and the comics companies had to refund the copies of issues that didn't sell, which could be hundreds of thousands of them. So in the 80s, the market shifted to comic shops (helped by some independent hits like TMNT). Comics didn't sell as many copies at first (the initial run of Watchmen sold something like 30,000 each) but they were guaranteed sales because the shops preordered them in the "direct market." (Only adults with transportation could go to said shops, so the content of comics became a lot more HBO.)
1990s: shops dominate, but the newsstand distribution still exists. So there was a boom starting with X-Men #1 and you could suddenly buy comics at Walmart. Several issues were multimillion sellers. Then, there was huge crash in the late 90s that began with Marvel and led them to the brink of bankruptcy.
Nowadays, the newsstand distribution is gone except for Archie digests, so individual issues that sell hundreds of thousands of copies no longer really exist. People buy collected editions from bookstores. A comic-shop hit today might be something like 50,000 copies. Marvel and DC are no longer "the big 2," it's actually more like Japanese Manga and Scholastic.
But record numbers of people are buying comics, in a lot of different formats. Somebody who lives on a secluded mountain can read them digitally or buy them on eBay, so comics are definitely not dying. Sales are probably down right now, however, because they are a luxury item and we are in a period of raging inflation.
