That saddens me so much, heissefeagerin. My cat is also an indoor cat, her "outdoors" is a small, screened-in patio area. She greets me at the door when I get home from dialysis or anywhere else. I can't imagine coming home to find her missing, especially now after the Cecil the Lion story.
I won't wish you condolences as there is always hope... not so long ago, though, we had very loved cat vanish for almost 6 months and she wandered back in one day... healthy and happy as ever! Don't give up my friend. Just keep the hope alive