I am looking for a way to combined obliterate and frostcythe into one button.... in a way.
Normally I am spamming obliterate but when I get a killing machine proc I want to use frostsythe. The issue I am having is often I am pressing obliterate so fast that I use the killing machine proc on obliterate instead of frostcythe like I wanted to. What I would like to do is have one button that cast obliterate if the killing machine proc is NOT up and cast frostcythe if the proc IS up.
You can't do [if: procc/buff/cooldown] macros. Not possible, sorry.
You can track it, but that's it. Considering DKs now have a (relatively) slow GCD now compared to pre-legion, this definitely shouldn't be an issue, even with mashing your abilities. I'd suggest getting either WeakAuras2 or TellMeWhen*, and just setting up an icon on your screen when the Killing Machine buff is active.
*You should really already have either of these, they are all-but expected these days. You're essentially putting yourself at a disadvantage for not having them as they are just so damn efficient compared to the default UI when setup properly.