Accurate orbital information might not be necessary or possible, if you can perform broad scanning that can quickly lock in your given target, but it certainly doesn't hurt. The issue is that even having an orbital track, because of the sats being so low in LEO, atmospheric drag will change your orbit rapidly enough that this information can get out of date quite fast.
Convenient and reliable fallbacks I feel are largely a solved problem for SpaceX. They've built their Starlink bus by reusing a lot of the software from the Falcon 9, Dragon, and Starship programs that already had to handle even greater levels of reliability.
Routing and retransmits are indeed quite a novel area for this kind of service. But the laser link will only be locked on one other peer satellite at any given time, and I don't think they plan on reorienting the sats in order to establish laser comms because of the effect it would have on drag as well as albedo. The former impacts service life per sat, and the latter has been a big rallying cry for Starlink opposition due to the impact it has on astronomy and the visible sky.
So if you likely can't reorient to retransmit, your only options are the peer laser link or the ground transit exit node, either or both of which might not exist, but I feel like you would just ack the packets on each hop to your peer and leave it at that.