A dissenting opinion: Writing a blog helps you organize your thoughts, improves your writing skills, and teaches you to make good arguments (and recognize bad ones). None of that requires having an audience. At least an audience larger than your friends and coworkers. If you like to write, don't stop writing because it's not "where the buzz is at". There's more to life than following trends.
You can also write in your blog for your great-great-great-grandkids -- family that hasn't been born yet. Or you can write as a way of organizing book material. Or you can write as a way to keep and share memories with just a few people. Blogging is an internal thing first, external second.
You think stuff we are producing these days will last? I'm dubious. Paper lasts a decent amount of time, but digital media?