If you’re just using 1 amp as your pedal platform, then you don’t need a MIDI cable. Simply hook up the Kemper into the Helix in 4CM and set up all the effects in the Helix however you want.
You’ll want to place an FX Loop block in the Helix as a replacement for an Amp block, since the Kemper is acting as your amp in this case. No need to do anything with the X block in the Kemper. You wouldn’t want to hook up the Helix into the Kemper as that won’t be optimal (in terms of flexibility), IMO. Plus, that would require MIDI programming. I’m sure you can find videos on YouTube on how to set this up. I believe Line 6 has a couple of them on their YouTube channel. You can also find this info by searching online.
Honestly, if you’re just wanting a quick replacement rig I would simply use the Helix until you get your amp back. This setup is more hassle than its worth if it’s not gonna be used frequently.