I don't believe they will. According to ACES, the new UHF Northwest system is currently getting some final bugs worked out of it. I've heard that the UHF NW system will include a fire dispatch, two fire ops channels, a public safety channel, and an EMS dispatch. From the initial participating departments, it will likely include (fire) Bellevue, Avalon, Ben Avon, Emsworth, Sewickley, Leetsdale, Coraopolis, and Moon, and (EMS) Northwest EMS and Valley Ambulance Authority.
It's really anyone's guess. I'm also hearing that the Pittsburgh 800MHz Type II system for city services will be abandoned within the next 5-10 years. This source told me that they are committed to UHF, and will not be going 800MHz.