Well personally, out of all the choices mentioned, cutting a hole in the cabinet's bottom, would be my last. The piping assembly was obviously improperly installed.
Removing the glue and unscrewing the top part wasn't exactly what Frodo suggested earlier.
I assume the glue was put there for the purpose of stopping a leak. So you now also have the decision as to whether you should replace that patched up leak.
I suspect you'll be getting other respondents opinions as to what your options are and what they would recommend. I have already offered mine, which would leave the assembly easily removable in the future, in case you find you have, or want, to replace that patched up connection.