Even without garbage-collecting the coroutine, we get a failed assertion in debug mode (but no crash with the assertion removed):

Python 3.11.0a2+ (heads/main:c8c21bdd19, Nov 21 2021, 13:58:01) [MSC v.1929 64 bit (AMD64)] on win32
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>>> async def f():
...     pass
...
>>> coro = f()
>>> frame = coro.cr_frame
>>> frame.clear()
<stdin>:1: RuntimeWarning: coroutine 'f' was never awaited
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
Assertion failed: f->f_frame->generator == NULL, file C:\Users\sween\Source\Repos\cpython2\cpython\Objects\frameobject.c, line 705