Here on the Devzone, we focus on the present and generally don't speculate in the future of our products. AFAIK we have no plans of discontinuing the nRF51 series any time soon. Please contact your RSM (regional sales manager) for a more detailed answer. If you don't have the contact information, please fill out this Sales Related Questions form to get in touch.
Please note though, that the nRF51 series are not recommended for new BLE products if that's what you have in mind. Their SoftDevices and SDKs are no longer being updated, so for a more polished and consistently updated product, please check out the nRF52810 or the nRF52832 instead.
