I lost my app source files, but have the app on my iPad
Simple answer is no.

Swift (and objective C) is compiled into machine code and much of the naming is thrown away and optimisation will also alter the control structure.

Experienced reverse engineers can get some form of code back but it is not very readable or useful in most cases.

When you start any coding project the first thing you do is set up source code control so you can take snapshots of code.

Note that the " wiped without my knowledge and with no warning" should be expected on any computer. Hardware can fail let alone errors an people mistakenly or deliberately removing files.