No, no, no, no.
Otamendi wouldn't have stopped a single goal we conceded against Leicester. We conceded vs Leicester because the team wasn't compact enough and we lost the second balls - that's why Guardiola had them do 2 hours a day practising defending that. That's why he mentioned it in his interview with Henry, in his pre-match press conference and in his post-match press conference.
1st goal, ball drops to Mahrez in acres of space in midfield - nothing to do with Otamendi's absence, everything to do with the team being too spread out.
2nd goal, ball drops to King because the team is too spread out.
3rd goal, Vardy is much faster than Otamendi anyway, if he can't keep up with Costa vs. Chelsea he's got no chance vs. Vardy.
4th goal, Stones back pass, nothing he'd have done to stop it.