and by taking some dubious cure from the town shaman, they turned into zombies
Depends on what happens with the Zombies.
Variant a) All Zombies attack and must therefore be killed -> the town is empty afterwards - no-one's there to trade with ...
a.1 : The key to the only shop in town is lost with the killed Zombie
a.2 : The key to the only shop in town can be gathered from the corpse of the dead Zombie -> dice roll of what TDE knows as "fear of the dead", don't know how this could be translated, and/or fear of fiddling a tiny metal key from a really stinking, ugly, rotting corpse -> dice roll for constitution (or something similar) -> if failed -> vomit, if not failed -> taking the key succeeds (plus, maybe, a drama point for that char)
a.3 : The key to the only shop in town is lost, but the lock can be broken or something similar
Variant b) All Zombies must be cured WITHOUT killing them - which means the characters must use stealth and be very, very, veray careful (or simply running away by sheer speed). And then a REAL cure must be found - or even better : Be mixed through the combining of inmgredients which must be collected first ...
b.1 : The Zombies must be lured into traps (cages ?) which hold them meanwhile the party is looking for a cure.
b.2 : Same as above, only with a limited time available to find the real cure.
That's what I'd be thinking of that.
And of course I'd grant the Variant b with MORE experience points, personally ...
Or/and maybe even with something SPECIAL the party couldn't get if all Zombies were dead ...