As far as I know, there is no possibility to disallow the drag & drop functionality.
I found an answer from Product Line Management to a similar request for Creo Parametric 2.0, which had been answered as: "This would be an enhancement" (as usual, without commitment to add the enhancement to a specific version)
Of course this request only stated "Drag and Drop behaviour for restructuring asm components is dangerous as it gives no warning to user if it is dragged accidently and even doesn’t show any status in model tree to identify restructured models."
It seems without any dramatic effects documented (like crashes, wrong geometry, inability to check in/out, etc...) the pure idea that a user might not be aware of what he had been doing, was not frightening enough to take immediate measures.
According to a colleague, models restructured in older releases in fact have been a pain when trying to check them in into Windchill PDMLink, but he mentioned that it should no longer be an issue with Creo Parametric 2.0.
The only report about an exit during restructuring I found, was due to a data corruption in the assembly - so it could have happened with other actions as well and was not specific to Restructure.
But if there is any reproducible scenario of restructure causing mischief, it should be reported to PTC Technical Support.
