To clarify, fonts don't propagate. A textstyle could though.
The easiest remedy would be to eliminate "simplex2.shx" from the support file search path and set FONTALT to whatever font you want to use as a replacement.
Then when the drawing opens, it won't find "simplex2" and it will substitute whatever you specify.
Another, more direct way would be to use a font mapping file. How to is explained in HELP.
Lastly, you could write a routine to check each drawing as it opens and physically change the font reference from "simplex2" to something else, or write a batch routine to perform this on multiple DWG files without even opening them. I think
ToolPac even includes a routine that could do the latter.