The result of any expression would still be assigned to a variable or function parameter that has a defined type, so it would be limited to that size. However, intermediate values could automatically use larger registers, the CPU's carry flag, or some other mechanism to expand the range.

It would be desirable that every expression either produces the mathematically correct result, or a runtime exception.

In many cases it would be easy for the compiler to limit intermediate results to some number of bits (since it knows the maximum allowed range for the final result), but it may be a problem to guarantee this.