Erlang (the language) can not run without OTP as OTP is essential to the runtime environment of Erlang. They are the same entity, which is why the official name is Erlang/OTP.

EDIT: an example to be more specific. The basic libraries such as the code server (in charge of loading the Erlang modules in the VM) are packaged as Erlang applications, which is an OTP framework construct. These parts of the OTP framework themselves are included in the Kernel application, and written in normal Erlang.