No, Yiddish is a Jewish language, with words that are specific to the Jewish experience. It is no different than modern Hebrew, except that it is regionally exclusive to Europe. The tzioinim claim that anything that evolves in golus is not Jewish – and that to them also includes much of halacha. We don’t define Jewish according to their standards.
Once we convert a name, it is ours – once a non-Jew converts, he is a Jew. That name has been elevated, for whatever historical reason, and that is the end of it. If all we have for a Jew who needs rachamei shamayim is a clearly non-Jewish name, we use it – but it is also a great time to give that person a real Jewish name. And if that name is from Yiddish or Judeo-Arabic or Ladino because the person wants to remember a relative, so be it.
I think yeshivish will die out now that the Internet makes it possible to learn proper English. In any case, you do not have a written version of yeshivish (or hymish), except when Purim rolls around.