SQS doesn't kill jobs - and I am not sure what you mean by you have code 'running in SQS' - what SQS does do, is to assume your job (which is running someplace other than SQS), has failed if you don't mark it completed within the timeout (Default Visibility Timeout) you set when you setup the queue.
Your job asks SQS for an item to work on (a message to process) - your job is supposed to do that work and then tell SQS that the job is now done (deletemessage). If you don't tell it it is done, SQS makes an assumption for you that the job has failed and puts the message back in the queue for another task to process.
If you need more time to complete the tasks, you can change the default visibility timeout to a higher value if you want.