Foreign tourist will still come...kenya is long haul destination for the rich.
Expect tourism from Asia to fill the gap that western tourism will leave. China are already the world biggest source of tourist. In the future..you'll see more indians, more chineses, more koreans, more eastern europeans, more arabs and such visiting kenya and other destination.
European tourist prefer beaches/wildlife/sun/sex/....we need to find out what chinese or indians prefer...i suspect wildlife..casinos..and some sun too.
Domestic tourist from Nairobi..will like you said...go for short vacations in surrounding counties.
Domestic tourist in US or EU will do the same..touring short haul destination.