Bergerie1
If you required a certain amount of fuel to get to the Seychelles and then have enough to divert to Mombasa and this put you overweight at the Seychelles surely by burning off fuel to get to the landing weight at Seychelles you would be below the legal requirement to reach Mombasa has a last minute incident closed the Seychelles airport.
I suspect the only legal solution would have been to reduce the traffic load ex Nairobi.