There are inserts you can use in stripped threads. One type is like a spring, made of wire shaped to replicate a thread. It need a special tap to tap the stripped hole and then another tool to insert the spring. Those are called helicoils.
The other type is a hardened sleeve with threads on the inside and the outside. The sleeve ones just have to have the stripped threads drilled out and then the sleeve cuts it's own threads as it's wound into place. It can be wound in using a bolt with a locknut. The advantage of the sleeve ones, apart from their ease of use, is that they come with fine or course outside threads, and because of the different threads, different outside diameters. It's an advantage to use the course thread in aluminuim because it gets more grip, but if space is limited you can use a fine thread one. The fine threads are fine in aluminium or cast iron or steel... Unfortunatly.. I don't know what they call those ones..haha. I've been using them for about forty years and always just ask for a rethreading sleeve and the local engiineering supply shop know what I'm talking about.
If it's a long head bolt you are talking about here then you need to be very careful to align the drill and then the sleeve when you wind it in, or the long bolt might not want to start into the sleeves thread afterwards without crossing. I've done it before by brazing a long shank onto a drill and then using the barrel and head as a guide to ensure the drill went in straight down the required line. Then I used a long bolt and locknut and again wound it into place at the bottom of the barrel and head using them as my guide.
If it's just an upper end short sort of bolt then it's not so critical and you will get it right by eye if you use a long bolt and locknut to wind the sleeve in.
And, if you haven't put any sealant on the new head gasket, or run the motor yet, then yes you can reuse the gasket.
