I was under the impression that Rust (and safe_ptr) deallocate at scope end, which could also cause framerate issues (unless you do ugly scope hacks).
I do agree that you're unlikely to bump into this issue, though.
You can just use delete, as you mentioned, it is a C++ only construct as far as I know.
For the std library smart pointer, you can get their value (the raw pointer), delete that then assign nullptr to the smart pointer. I would consider this a code smell, and ask hard questions of the authors of such code.
The simplest thing to do is to add new scopes. You can introduce as many blocks with { and } as you like. It is a common pattern to lock a mutex with a class that releases the mutex in its destructor (and acquired it in the constructor). The std library includes std::lock_guard[0]. To insure the smallest possible use of the lock a new scope can be introduce around just the critical section and the first line of the block can pass the mutex to the scope guard and it should be about as small and efficient as can be, while be exception safe and easy to write. Hopefully this is also easy to read.
You can introduce new scopes with std::shared_ptr or std::unique_ptr as well. This seems common and reasonable.
[0]https://github.com/libgdx/libgdx/wiki/Memory-management#obje...
With C, C++ and Rust allocating memory often boils down to calling something equivalent to malloc and free. While the cost is not precisely known all modern OS provide guarantees are the time to execute relative to the size of the amount requested. This is almost always such a simple and fast operation that allocation is what gets optimized only after the algorithms and data structures have been tuned and this is a known bottleneck. Many application never get to the stage of optimizations (Games almost always do, stupid fixed time frame budget).
Consider the amount of work the GC does and understand why any GC is generally considered no-deterministic: https://blog.golang.org/go15gc