Trying to create a Japanese word by combining others, does this work?

Hello, I've created an angel character based off the concept of lonely death / kodokushi. I tried to combine kodokushi 孤独死 and tenshi 天死 into one word: kodokutenshi 孤独死 - I swapped the shi kanji in tenshi with the shi in kodokushi so its more focused on death than being a 'messenger'. So, supposedly, it should mean "Lonely angel of death" or something similar

Does this word actually work in Japanese or have I created gibberish?

well, 孤独死 and 天使 are words, 孤独死 being a compound word of loneliness and death, and while tenshi does share a sound, when you swap the kanji out it changes the meaning. If you were to say "kodokutenshi" aloud it may be understood as "lonely angel," but if you try to change the kanji to 孤独天死 would not carry the double meaning you intend and it would look more like "lonely heaven death."

so, it's not a Japanese word, but you can get as creative as you want if you're just playing around or don't mind explaining your intention.

My two cents:

孤独死 sounds to me something akin to "death by loneliness", similar to the actual Japanese word 過労死 "death by overwork".
If you were to use 孤独使 as a name for an angel, my first instinct is to read it as "kodoku-zukai". However, this being your story, I agree with @nice gaijin that you can call the character whatever you want, however, at some point it would probably be wise to clarify for the reader how to pronounce this name, which could be accomplished in a number of ways. I also agree that your intended double meaning is not self-evident. But that doesn't stop you from explaining it in your narrative somehow so that it becomes understood within the course of your unfolding story.

Actually, 孤独死 is a really used word, meaning lonely death/dying alone, i.e., it's 孤独に死ぬ, unlike 過労死 (過労で死ぬ).