are they accessing any pages after this query? I assume all blocked IP will not be able to access any questions or answer. I dont think your site will be showing any output for their search query. If they are able to access any QA then let us know, that is bug in Q2A.
If this kind of attacks are more then it will consume your server resources(RAM, CPU) and slow down server. This will have impact on your real users, they may see site loading slow. Many time hackers are only interested to bring down site, if they are not able to hack.
If you see this kind of issue again and again then I recommend you to use cloudflare.com like services. They know how to protect from DDoS attack. They will take care of such attacks at DNS level, even before it reaches your site.
Let us know how your are able to fix this.