Can my Thai partner go on holiday whilst we are awaiting the decision on the Australian provisional marriage visa?

It is at the discretion of the Australian visa officer, but in my experience, the answer is yes. This is because the decision can take anything between 4-7 months. It is a long time to be away from your Thai partner which the Australian Embassy tend to take in to consideration, so if the documents are presented correctly, a tourist visa would normally be awarded.