Assuming you are in England, Wales or NI, an offer made and accepted is not binding on either party until exchange.
You make an offer based on what you think the house is worth given what you believe you would be getting based on the viewing(s) you have done.
Then the period between offer accepted and exchange is for you to gather as much information as you can about what you would actually be getting, including clarifying exactly what the sellers plan to remove.
So take the "should" out of it. Take the emotion out of it. Maybe they should leave the rads and maybe they shouldn't, but since you have not legally committed to anything yet this is just a pricing discussion.
All that really matters pre-exchange is whether more accurate information about what you will be buying changes what you think the house is worth.
If it does, you make a new offer. They will either accept it or not.
"We assumed the rads would be left and the house required very little decorative work and that is reflected in our original offer. As that is not the case we are changing our offer to X to reflect the cost and time of buying and installing replacements, the risk of finding good contractors for the work and possibility the cost, time and risk of redecorating after."
If they don't accept it but still plan to take the rads, it is then with you to decide whether the house is still the one you want at a price you are prepared to pay.
This isn't throwing your toys out of the pram; literally the whole point of gettiing this info from the seller before the sale is finalised is so that you can resolve any misapprehensions about what is included.