Both are nothing special even with edo and this is why.
Its true if deidora uses c0 he would just regenerate but people with great defence and sealing ability should withstand the blast then seal him during his regeration process.
Secondly the myth about gai being invinsible if he is an edo in gates imo doesn't make sense. We saw that the 2nd mizukage was extremely exhaused when he used his strongest technique, joki boy. Similarly, mu still suffer the effects of splitting which is that he cannot use dust release anymore. No different to itachi still bleeding from his eyes when he uses amaterasu. There are still clearly draw backs when a character uses their signature move and i see no reason why this doesnt apply to gai. In 8 gates and edo form, he obviously wouldnt die but the gates dont last forever, and i believe he would feel the effects of the gates no different to the characters that ive named feeling the effects of their signature move