If you don't stop streaming, then when the Mini Microphone is turned off, the CP900 Sound Processor will keep searching for a signal from the Mini Microphone for the next 5 minutes. Apart from using up a little extra CP900 battery charge, the main problem is that the CP900 will remain in the mixing ratio set for accessories. In other words, if you have a 100% mixing ratio set, then when you turn off the Mini Microphone, you will then hear NOTHING from your CP900 microphone for the next 5 minutes.
This scenario would be obvious to you as a recipient, but it is not so obvious if the mixing ratio is set to 2:1. This is because you may not realise that you are only receiving stimulation at half the volume that you should be, for 5 minutes.