PowerShell script for SharePoint Online to reset all subwebs, lists, and list items in a web.

O365WebInheritanceReset.ps1

[CmdletBinding()]
Param(
    [Parameter(Mandatory=$true, HelpMessage="This is the URL to the SharePoint Online site where you want to reset inheritance.")]
    [string]$Url, 

    [Parameter(Mandatory=$false, HelpMessage="If true, all subwebs will be reset as well.")]
    [Boolean]$Subwebs,

    [Parameter(Mandatory=$false, HelpMessage="This is the path to the DLLs for CSOM.")]
    [string]$CSOMPath
)

Set-Strictmode -Version 1

If ($Subwebs -eq $null) { $Subwebs = $false }
If ($CSOMPath -eq $null -or $CSOMPath -eq "") { $CSOMPath = "." }

Add-Type -Path "$CSOMPath\Microsoft.SharePoint.Client.dll" 
Add-Type -Path "$CSOMPath\Microsoft.SharePoint.Client.Runtime.dll" 

function ResetItem ([Microsoft.SharePoint.Client.ListItem]$currentItem) {
    $currentItem.ResetRoleInheritance()
    $currentItem.Update()
}

function ResetList ([Microsoft.SharePoint.Client.List]$currentList) {
    $clientContext.Load($currentList)
    $clientContext.ExecuteQuery()

    Write-Host $currentWeb.Title: $currentList.Title

    $query = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
    $items = $currentList.GetItems($query)
    $clientContext.Load($items)
    $clientContext.ExecuteQuery()

    $items | ForEach-Object {
        ResetItem($_)
    }
    $currentList.ResetRoleInheritance()
    $currentList.Update()
    $clientContext.ExecuteQuery()
}

function ResetWeb ([Microsoft.SharePoint.Client.Web]$currentWeb) {
    $context.Load($currentWeb)
    $context.Load($currentWeb.Webs)
    $context.Load($currentWeb.Lists)
    $context.ExecuteQuery()

    Write-Host $currentWeb.Title: $currentWeb.Url

    $currentWeb.Lists | ForEach-Object {
        ResetList($_)
    }

    If ($Subwebs) {
        $currentWeb.Webs | ForEach-Object {
            ResetWeb($_)
        }
    }

    $currentWeb.ResetRoleInheritance()
    $currentWeb.Update()
    $context.ExecuteQuery()
}

$psCredentials = Get-Credential
$spoCredentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($psCredentials.UserName, $psCredentials.Password)
$clientContext = New-Object Microsoft.SharePoint.Client.ClientContext($Url) 
$clientContext.Credentials = $spoCredentials 

If ($clientContext.ServerObjectIsNull.Value) { 
    Write-Error "Could not connect to SharePoint Online site collection: $Url"
} Else {
    Write-Host "Connected to SharePoint Online site collection: " $Url -ForegroundColor Green        
                
    $web = $clientContext.Web
    ResetWeb($web)
}