Hello jashin, I'm going to repost an old comment, there is still continuity for the game
One idea for the game would be to create zones through which the syahata would have to pass to complete the mission objectives and in these zones there would be monsters very characteristic of that habitat. for example: syahata will do a mission in the swamp, the monsters would be characteristic of the environment, mutant crocodiles, mutant frogs, flies or other flying insects and a mud monster as a boss
another example: syahata has to go through an area of the city, more specific in alleys, there may be characteristic things in this area such as other variants of infected zombies, mutant cockroaches, another variant of rats and the boss of this area may be a giant dog
It would be an interesting idea for the continuity of the game
Since the game has already ended, there would still be other tasks for Syahata now as a member of a special force, or you could use this as an idea for a new game