Well, with the horses, in theory, he doesn't have to walk much and could still be effective in fights.
I also think it is entirely possible, maybe even likely, that Negan will eventually be the person we see physically leading battle/protection and Rick will be more of a strategic/diplomatic leader that remains in Alexandria and maintains order while working with the leaders of the other civilizations. Right now we are led to believe those are The Kingdom/Ezekiel, The Hilltop/Maggie, The Saviors/Dwight. But maybe they have met more over the two years. Michonne not being in this issue leads me to believe she is at The Kingdom, Jesus I believe is more a member of member of the Hilltop, and I cannot see Dwight letting Negan back. This assumes Negan is eventually allowed to rejoin civilization but I think that he is best suited for that role of the known Alexandria members.
TL;DR Rick remains a strategic/diplomatic leader even if he is hampered physical by his leg. And he can ride horses.