Well, the injury is unfortunate but it really is an opportunity for him to take a hard look at what he's doing and refocus his channel. His current set up is totally unsustainable. He creates way more work for himself than is necessary with the daily uploads, which leads to repetitive, junk content. He goes for the easy fluff when pressed, like constantly talking about himself, filming endless coffee drinking shots, or overexposing elements of his family life. If he were smart, he'd use this time to expand his engagement with his audience, diversify his content, and make videos they'd like to see, not videos that are easy for him to make.
I mean, he has a running channel based in Colorado - there's a ton of stuff he could do locally that could grow his channel even when he's injured. He could interview other top runners or running groups, do an in-depth discussion of running trails he's run, visit with college/high school teams, or talk with people in the running shoe industry. Heck, why doesn't he just interview the people at his local running store to hear what they think about the latest shoes. (On this last point - I find it amazing that a channel that is so focused on running shoes has only once (that I know of) had an discussion with someone from a shoe company or from running retail about design and upcoming releases. It's like he's resistant to doing anything more in-depth on the topic that is effectively the "bread and butter" of his channel.)
All that said I'm skeptical he will do any of it. He seems totally uninterested in the quality of his daily uploads and has even told other You Tubers that the key is not in putting out quality content, but to constantly put stuff out. As in, every day, same old junk is better than anything that would require some effort or creativity. Here's a tip - you may think that, but your stalled subscriber numbers are telling you otherwise.