If the sensor is unresponsive, sometimes it is just enough to press the wake-up button to get it working again. If you just reset it (without proper disassociation from Homey) you can’t add it again until you removed it. You have to remove it from Homey, then reset the device and then you should be able to add it again.
Zigbee devices that are powered by 220 are mostly capable of acting as a repeater. For instance Zigbee plugs or Hue or Trådfri bulbs. Or you could buy a specific Zigbee repeater.
You can reset the Zigbee network, but if you do that, all devices and settings will be gone and you have to add every device again. Also every flow associated with a disappeared device has to be repaired.
I myself have no experience with the Xiaomi door/window sensors, only with the temp sensors.