Is Aperture compatible with High Sierra upgrade process? If I update the newest software version to 10.13 and apply all security patches, will it delete my Aperture program?
IF you bought Aperture from the Mac App Store, you should be able to re-download it from there from the Purchases tab, even though it’s no
  longer available for sale. (However, I never did, so I can’t confirm
  this.)


I can confirm this is possible to download on High Sierra still and that it is in the Purchases tab.

If you can't find it you may have downloaded it on a different account or it may be hidden, you can unhide purchases from the My Account link.