Hey, sorry to hear that. Could you describe more in detail why the building option disappeared? Was it available for some time before disappearing? Did you cancel the building at one point? Anything helps. Meanwhile, there is no way to regain the ability to build the Imperial Seat UNLESS you modify the mod code. Here's what you have to do
1. Locate on your computer where you installed Europa Barbarorum II
2. Find data/export_descr_buildings.txt and make a copy of it, and store it somewhere safe. You want this backup version in case the modification goes wrong
3. Open the mod's export_descr_buildings.txt and Ctrl+F (use the search function) to quickly locate this code line
Code:
hay_imperial city requires factions { f_hayasdan, } and not building_present govallied and region_religion rel_c 30 and event_counter ecHayasdanImperial 1 and event_counter ecHaySecondCapital 1 and hidden_resource caucasus or hidden_resource eastern or hidden_resource anatolian
Do you see the red highlighted code? That one forces you to be able to build the Imperial Seat only when the size restriction is obeyed.
4. You need to delete the red underlined code and then save the file. The result should look like
Code:
hay_imperial city requires factions { f_hayasdan, } and not building_present govallied and region_religion rel_c 30 and event_counter ecHayasdanImperial 1 and hidden_resource caucasus or hidden_resource eastern or hidden_resource anatolian
5. Once you load your campaign, the Imperial Seat should be available in ALL cities formerly under the Persian Empire. You can now build it without worrying about restrictions.
It sounds like you're pretty deep into your Hayastan campaign, so it would be a shame to restart it due to a scripting limitation. This modification will salvage your campaign, but it would give you too much power since the Imperial Seat gives very good recruitment, as well as ruin the immersion since the Imperial Seat is not supposed to be built everywhere. If you want to make this building more restrictive, you can replace that same code line
Code:
hay_imperial city requires factions { f_hayasdan, } and not building_present govallied and region_religion rel_c 30 and event_counter ecHayasdanImperial 1 and event_counter ecHaySecondCapital 1 and hidden_resource caucasus or hidden_resource eastern or hidden_resource anatolian
with
Code:
hay_imperial city requires factions { f_hayasdan, } and not building_present govallied and region_religion rel_c 45 and event_counter ecHayasdanImperial 1 and hidden_resource caucasus or hidden_resource eastern or hidden_resource anatolian
or
Code:
hay_imperial city requires factions { f_hayasdan, } and not building_present govallied and region_religion rel_c 30 and event_counter ecHayasdanImperial 1 and hidden_resource royal_core and hidden_resource caucasus or hidden_resource eastern or hidden_resource anatolian
You can choose which restriction makes more sense to you. The first one requires that you reach 45% Eastern Imperial culture, which is achieved by building a level 2 foreign military colony and waiting for the culture to convert. The second one restricts the Imperial Seat to any "royal_core" province. Basically, provinces that were significant individual kingdoms at some point in the past or present. These provinces are:
Nikaia
Sardis
Pergamon
Antiochea
Kutatsi
Msteilika
Kabalaka
Shamusat
Arbela
Sousa
Seleukia
Persepolis
Ekbatana
Again, do whatever you want to do to salvage your campaign