Error handling on network call failure on multiple-component page

If I have a page with multiple panels or widgets, which get data from different REST calls and one of them fails,

• a) is it better to show an error message inside just the panel(inline error message), and continue to show other panel data? This way, user has access to as much data as possible?
• b) show a dialog popup for the whole page.

What is best practice? I think a) is better than b). Some of the questions I have if i choose a)

• Say I have 3 panels and all three calls fail (server down).. check this scenario and show an overall error? Or even in this case, each panel shows an error message (albeit they may be same error reason)?
• Should each panel have a separate 'refresh' option? to retry? Or should I let the users do the browser refresh to retry?
• In case of a dashboard with several widgets.. if the error is inlined inside a widget, the user may not even see it, unless he wants data from that widget.. Is that acceptable? Or should the user be made aware that some part of page did fail?