Conditionally Replace Default Null Values from Left Join - sql

Question

I am joining 3 tables. In tables 2 and 3, records do not exist for some of the IDs in table 1. This of course, yields null values for these instances in my joined table.
I know I can replace these nulls with coalesce, but I don't know how to replace the nulls conditionally. In my reprex below, I would like to replace a null with an ID's max total (if an ID has a non-null total under a different job title) or replace a null with 0 (if an ID has null totals under both of their job titles).
Reprex code below:
/*sample table a (contains full data - 2 records for each ID)*/
data table_a;
input id title $ region $ calls;
cards;
1 manager south 30
1 agent north 20
2 manager west 20
2 agent south 25
;
run;
/*sample table b (missing an agent record for ID 1 -- will result in null total sales for ID 1's agent record in joined table)*/
data table_b;
input id title $ sales;
cards;
1 manager 20
2 manager 5
2 agent 3
;
run;
/*sample table c (missing both records for ID 2 - will result in null total_leads for ID 2 in joined table)*/
data table_c;
input id title $ leads;
cards;
1 manager .
1 agent 10
;
run;
/*join tables*/
proc sql;
create table reprex as
select a.id,
a.region,
a.calls,
a.title,
coalesce(b.total_sales, 0) as total_sales, /*this replaces all nulls as 0, but I'd like to replace
b.sales, them conditionally */
coalesce(c.total_leads, 0) as total_leads,
c.leads
from table_a as a
left join (select sum(coalesce(sales, 0)) as total_sales, sales, id, title from table_b group by id) b
on a.id = b.id and a.title = b.title
left join (select sum(coalesce(leads, 0)) as total_leads, leads, id, title from table_c group by id) c
on a.id = c.id and a.title = c.title;
quit;

Answer 1

Ended up nesting subqueries to get what I was after:
proc sql;
create table reprex as
select id, region, title,
calls,
case
when max_total_calls is null then 0
else max_total_calls
end as total_calls,
sales,
case
when max_total_sales is null then 0
else max_total_sales
end as total_sales,
leads,
case
when max_total_leads is null then 0
else max_total_leads
end as total_leads
from
(select *,
max(total_sales) as max_total_sales,
max(total_leads) as max_total_leads,
max(total_calls) as max_total_calls
from
(select a.id, a.region, a.calls, a2.total_calls, a.title,
b.sales, c.total_leads, c.leads
from table_a as a
left join (select sum(coalesce(calls, 0)) as total_calls, calls, id, title from table_a group by id) a2
on a.id = a2.id and a.title = a2.title
left join (select sum(coalesce(sales, 0)) as total_sales, max(coalesce(sales,0)) as max_sales, sales, id, title from table_b group by id) b
on a.id = b.id and a.title = b.title
left join (select sum(coalesce(leads, 0)) as total_leads, leads, id, title from table_c group by id) c
on a.id = c.id and a.title = c.title)
group by id);
quit;