I'd suspect that's not going to work. I don't have experience specifically with this issue, but I've seen something similar on the email side, where using a variable in the href omits it from the text-only version of the email. My thoughts are that the value isn't directly there (it's interpreted when Marketo puts it all together to display to the end-user) and so it's not "searchable".
This might not answer your question directly, but Im hoping it might address the underlying issue of editing the links and that getting messed up. There might be a safer way to help your users edit the links without pushing it out into a variable (where you trade use-case issues w/ performance).
Here's a few steps that might simplify (error-proof) the whole link-editing process.
If you start by clicking on the link you'd like to edit (this is where most folks just delete the text and/or paste new stuff over it) in the WYSIWYG (no need to highlight/select anything) - that will "activate" the link icon [box] in the editor. If you click on that link icon, you'll get a pop-up which helps to separate the pieces of that link to help prevent styles, etc getting ripped off the element. You can paste you new URL here and even update (copy/paste from MS Word into the Display Text box for a happy crowd!) the text with no issue. If you're in the more "power user" or "advanced" settings, there another tab there that'll allow you add inline styles to the link element, but individually (so the users could copy/paste "chunks" of CSS worst case scenario to make style changes when needed).