I feel like a post like this is the engineer looking for a way to say ‘It won’t work’ to their boss.
Based on what do you make this statement? ASP.net is a preprocessor. It generates HTML. The web spider only sees the output, not the raw code. So it’s only ‘a web spider’s worst nightmare’ if your OUTPUT is poorly organized.
“If we switch from wordpress to .aspx will it affect SEO” (title)
As @TechnoBear says, Search results are based primarily on the content.
Now, that said; in the short-term, yes, rewriting your entire website to a different file structure will cause an ‘SEO’ disruption - you’re changing all of the pages, so the search engines will have to adjust to the idea that ‘this old page stopped getting views! … but this new one is getting views…’