So these fears are just because its 9 years old, and not because there's any problems? Ford designed the battery to outlast the vehicle. The only manufacturer that has hybrid battery longevity issues is Honda. Ford has an exceptional track record with their battery longevity. I've only ever heard of 2, maybe 3 battery failures, and I'm an admin and/or moderator on several automotive websites. Even at that, one of the batteries that was replaced, I wasn't convinced was really bad. I thought there was another issue with the vehicle that the mechanic was blaming on the pack.
Hybrid drivetrains are still relatively new technologies, and many mechanics just don't know that much about them. Fortunately, most of the hybrid specific known issues can be fixed in your own driveway relatively cheaply if you're moderately handy. I can say this for a fact, as I own and drive a 2008 Escape Hybrid 4wd.
That all being said, Welcome to the FEH owners club! As the proud owner of a new FEH, there's a few things that you should pay particular attention to...
1. While the hybrid battery pack will likely outlast the car, the 12v battery under the hood will not. Mysterious problems will crop up when this starts to fail, and battery testers at most mechanics shops and auto parts stores cannot properly test it. It is possible for a battery that tests as "good" to cause problems in an FEH, as this 12v battery's sole job is to power the computer system and vehicle controls. My recommendation is if the date code on the 12v battery is 5 years old or older, replace it... even if you aren't having any problems. If the battery is less than 5 years old, load test it. If it does not test as 95% or better, replace. If the tester comes up as "Charge before testing"... REPLACE. The battery should always be at 100% charge, as all it does is power the computer and relays.
2. 2005-2008 FEH's have a separate air filter for the cooling system for the battery pack. In the rear cargo area, on the left wall is a small removable panel. Under it is another black panel. Remove it and check the filter. This filter should be changed every 10K-15K miles, If you're going by the oil life monitor, you will replace this filter every other oil change. This filter is about $5 if you order it on RockAuto.com. Personally, I replace it at every oil change.
3. The engine thermostat. Since you can't get into electric mode until the engine warms up to operating temperature, a properly working thermostat is imperative. The thermostat is designed to fail in the open position, so as it ages, it starts to open earlier and earlier. Take a glance down there. If it looks like it still has the original hose clamps on the hoses going to the thermostat housing, I'd replace it.
Well, that's enough to get you started on the right foot... If you have any questions, just ask.