I can assure you that a PanelView, configured with standard tag access, that loses its network connection or suffers a power problem while a momentary button is pressed, will absolutely leave the target bit in the pressed state. This is also true for every single touchscreen product on the market that uses Allen-Bradley's tag data access protocols. And true for any other request/response protocol (Modbus, GE SRTP, Siemens pg). This topic has a pretty extensive discussion of the issue.
The bottom line is that momentary buttons that cannot be allowed to suffer this kind of failure must use an I/O protocol or have some heartbeat from client all the way to the PLC. I/O protocols repeat the bit status on a schedule, and the PLC itself notices when the schedule is broken. Modern Panelviews offer DeviceNet and ControlNet with scheduled I/O, and Classic Panelviews also offer AB RIO and scheduled Ethernet/IP. Other brands (like Siemens and C-More) also offer scheduled Ethernet/IP (aka Class 1 connections).