The heat, used wisely at a low and controlled level is not going to cause a issue. The old compromised finish will soften and render itself easily removable long before any threats to the wood substrate occur. I have used heat guns on marine brightwork on highly sensitive, expensive joinery and components for many years and the only time it has potential to cause a problem is when too much heat is used and/or it is concentrated in one local spot too long. I have an old Kodak 3A 5x7 view that I stripped with this method many years ago and it was just fine. It will not hurt the wood unless a person is careless and simply burns the wood because of poor technique.

Soy stripper is a superb stripper and is extremely safe to substrates. It is not a weak green product. Soy stripper is highly effective and is far safer for sensitive hardwoods than a standard chemical based stripper.