Hi AviA,

I had faced similar issues in past and didn't not find any better solution than to use two tables, one only with single column  and other with multiple columns.

Check the code below.

-----------------------------------------------------------------
Visualforce Page
-----------------------------------------------------------------
<apex:page id="pg" controller="tst123" >
    <apex:form id="frm">
        <apex:pageMessages id="theMessage"/>
        <apex:actionStatus id="sts"  layout="block">
            <apex:facet name="start">
                <apex:outputLabel value="Loading..." styleClass="loadLabel"/> 
            </apex:facet>    
            <apex:facet name="stop"  />
        </apex:actionstatus>  
        
        <apex:pageBlock >
            <apex:commandButton action="{!reRenderTbl}" value="reRender Table - With Status" reRender="frm, theMessage" status="sts"/>
            <br/>
            <apex:commandButton action="{!reRenderTbl}" value="reRender Table - Without Status" />
        </apex:pageBlock>
        
        <apex:pageBlock id="pbTable">
            <apex:outputPanel rendered="{!oneRow}">
                <table class="list" id="tableWith1Column">
                    <tr>
                        <th id="tst1"> Header Row - Column #1 </th>  
                    </tr>
                </table>
            </apex:outputPanel>
            
            <apex:outputPanel rendered="{!NOT(oneRow)}" >
                <table class="list" id="tableWith2Column">
                    <tr>
                        <th id="tst1"> Header Row - Column #1 </th>                
                        <th id="tst3"> Header Row - Column #2 </th>
                    </tr>
                </table>
            </apex:outputPanel>
        </apex:pageBlock>
    </apex:form>
</apex:page>
-----------------------------------------------------------------
Controller
-----------------------------------------------------------------
public with sharing class tst123
{
    public Boolean oneRow {get; set;}
    
    public tst123()
    {
        oneRow = true; 
        apexpages.addMessage(new apexpages.Message(ApexPages.Severity.INFO, 'in CS_rerenderIssue - oneRow : '+oneRow));
    }
    
    public void reRenderTbl()
    {
        oneRow = !oneRow ; 
        apexpages.addMessage(new apexpages.Message(ApexPages.Severity.INFO, 'in reRenderTbl - oneRow : '+oneRow));
    }
}
-----------------------------------------------------------------

What I also felt is that in if you rerender columns dynamically in a visualforce page(which is rendered as PDF) then all the table formatting is lost. So this approach was very helpful for me.

Another option/solution would be is to use a wrapper class List to control the columns, but that makes code bit complicated; on the other hand it also gives you more control.