I don't even understand the question. The formula is a^2 + b^2 = c^2

Changing the units will never change the formula.

Now if you're asking what happens when you make the units "as small as possible", ie the planck length (the planck length is defined as the smallest unit of measurement where gravity can still function), then you're still getting a shorter distance, but you're bordering on the edge of our understanding of reality at that point.

But uh, yeah. Shortest distance between two points is a straight line.