I would´nt really compare the Petar Kreshimir-class FACs with the Gothenburg-class corvettes. Size, and crew, wise they may be compare but not in performance and tasks. With its radar, sonars, FCS, EW, weapons etc Gothenburg is more comparable with a frigate. It lacks the long-range SAMs and endurance though due to its size.
As I wrote before. Two of the ships (HMS Sundsvall and HMS Gävle, wich have been offered to Croatia) have recently been trough MLU. This modernisation included modifications so that they could operate in internationell missions, work in warm climates and have longer endurance etc. They are also part of the EU internationell rapid deployment force and one of the ships (HMS Gävle) is currently patrolling outside the Lebanon-coast as part of the UN-force. She has performed excellent and just recently got her mission extended down there. So there´s no need to worry about these ships not working in the adriatic sea conditions.
Don´t know if Croatia has such large waters to patrol, but looking at the map it rather seems that the waters surrounding Sweden (Baltic sea and Gulf of Bothnia) is rather similar, if not even bigger. But offcourse, a bigger patrol ship is preferred at such duties. But in that case you buy a big patrol ship, not a frigate.
I don´t think this offer is on the table if not Croatia chooses the Gripen, cause we are planning on keeping them for another 15 years (they were just modernized). IIRC the plannes for the swedish navy is to have 5 Visby-corvettes, 4 other corvettes (either 4 Gothenburg or 2 Gothenburg+2 Stockholm-class) and build 2 frigates (that will probably replace 2 corvettes). So if Sweden wanted to offer Croatia corvettes without the Gripen it would be either the non-modernized Gothenburg or the recently modernized, but older Stockholm-class corvettes. The only reason these Gothenburg were offered was cause they can operate in the adriatic right now and that HMS Gävle is allready down there...