Businesses with accessible property are easy targets. First off people would cancel their bookings. Then trump jnr would have to beef up security, that would cost a lot. Then they would drop their prices to attract customers. Its a spiral that would break his heart. His hotel businesses would urn into militarised compounds and, as stated, it would cost nothing and nobody would get hurt.
There is so much to unload there that it is impossible to know where to start but insurance alone would cover any losses in those circumstances i.e. they would payout all projected profits, then there is the responsibility of the host country for security, in situations like this [ e.g. twin towers] there is a fortune to be made in insurance claims and government culpability, no businessmen ever go into things like this without a fallback position, lawyers always make sure those bases are covered...in fact lloyds of london would more than likely be picking up the lions share of that tab...
...You can rest easy in knowing trump and others are well insulated from such things, heck trump may even be setting up his business plans around such acts while collecting money he could never hope to make otherwise...
...You'll be gloating and he'll be counting his money