Insurance claim

you've got your head on straight. 100% do not release the car to them for anything. they want to gripe and moan, tell 'em to send a field adjuster out to take pics and write up an estimate.

if you want to keep the car, try not to have it totaled out. if it goes salvage you'll need to jump thru all the hoops to get the title cleared-- brake and light inspection, vin inspection and they may also insist on a 2nd party safety check and evaluation. all of which you guessed it, you have to pay for.

then, at the end of that, allstate will probably bounce you from coverage or up your rates considerably. some companies won't insure salvage titles, others will only do PLPD

if you DO want it totaled, find the absolute closest and best comps to what you have. i'm not sure what allstate's radius is, but some companies only will allow for comps within a specific range or geographical area.

no matter how you decide, do not release the car until you have a check in your hand.