I’m a fluent, everyday user of ASL—it’s my primary language. Translating is also a lifelong hobby of mine.
I would look at the semantic content first. This line: How far we’ve fallen… has several layers of possible meanings, so what does it mean to you? Some possible meanings are:
—“how far (deep?) we’ve fallen (in love?)” or
—“how far (emotional distance?) we’ve fallen (apart?)” or
—“how far (directional distance?) we’ve fallen (from our original place?)”
—“how far (depth?) we’ve fallen (broken down)”
As for: when the road before us leads apart—it’s a bit more straightforward but still, you have to decide if it’s:
—“when the road (future) leads (guides) us apart (in different directions)” or
—“when the road (paths) leads (travels) us apart (two different options we could take)” or
—“when the road (paths) leads (forces) us apart (in different directions)”
—“when” could even be translated as “even though”
In ASL, you’d want to sign the correct conceptual sign, not the English word. If you signed “fall” like if someone slipped and fell, in all possible options, it’d be wrong. The line has no relevance to someone literally taking a fall.
Example: There’s a song line by Wire Train: “And Charles Atlas stands upon the beach upon his head and says I will not fall…” To sign the literal sign for “fall” here would be accurate.
When you decide what the underlying semantic/connotative meaning is, that will influence your translating decision. Decide what the whole line means to YOU then go from there.