Yeah, this is a really interesting question.I would be thinking about:
1. An open letter from the CEO of your hotel chain that's hosted on your website. Something that shows empathy with customers who are considering booking your hotel but are majorly put off by the terrorist events. A letter that details out everything the hotel has done in the community, to help the victims and to increase security since it happened.
There's no escaping the fact that when customers are researching this hotel via Google, they are going to come stories detailing the terrorist event. Perhaps the only way you can combat that is by detailing your side of the story and showing an openness to tackle the issue head on.
This could also work well from a PR perspective because you could use the content to contact journalists and publications who covered the original story. PLUS from a reputation management perspective, you might be able to replace some of those news stories with an updated story on how you're handling the situation.
2. Revisit your deals, offers, and partnerships.
If the hotel is struggling with sales, no matter how dire the situation, travelers are always going to be attracted to good offers and deals. Maybe you need to test ramping up your offers and promoting them via affiliates?
Opening up an affiliate network is perhaps one way of creating an immediate boost in sales.
3. Find and reward your current advocates and returning customers.
Have you got customers that have been coming back for years and years?
How about customers that have CONTINUED to return, despite the events?
You need to thank these people. Reward them. Speak to them and hear their stories about why they returned to you. This will help you to create your strongest messages.
In addition to this, putting a strategy together to highlight great customer feedback, reviews etc. from this point forward is something I'd recommend.
Good luck and thanks for posting this question.